[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.04,0:00:03.17,Default,,0000,0000,0000,,在这个视频中 我要做几个
Dialogue: 0,0:00:03.17,0:00:07.20,Default,,0000,0000,0000,,把直线方程化成斜截式的例子
Dialogue: 0,0:00:07.20,0:00:08.07,Default,,0000,0000,0000,,就算是复习
Dialogue: 0,0:00:08.07,0:00:10.70,Default,,0000,0000,0000,,这就是说把直线方程化成
Dialogue: 0,0:00:10.90,0:00:21.29,Default,,0000,0000,0000,,y=mx+b的形式 m是斜率 b是y截距
Dialogue: 0,0:00:21.29,0:00:23.58,Default,,0000,0000,0000,,我们做几个这样的问题
Dialogue: 0,0:00:24.32,0:00:27.89,Default,,0000,0000,0000,,题目说有一条斜率是-5的直线
Dialogue: 0,0:00:27.89,0:00:33.93,Default,,0000,0000,0000,,所以m=-5 它的y截距是6
Dialogue: 0,0:00:34.32,0:00:36.40,Default,,0000,0000,0000,,所以b=6
Dialogue: 0,0:00:36.40,0:00:38.32,Default,,0000,0000,0000,,非常简单
Dialogue: 0,0:00:38.32,0:00:47.39,Default,,0000,0000,0000,,直线的方程是y=-5x+6
Dialogue: 0,0:00:47.79,0:00:51.25,Default,,0000,0000,0000,,不赖嘛 做下一题
Dialogue: 0,0:00:51.25,0:00:57.02,Default,,0000,0000,0000,,直线的斜率是-1 经过点(4/5,0)
Dialogue: 0,0:00:57.42,0:01:00.56,Default,,0000,0000,0000,,题目给了斜率 斜率是-1
Dialogue: 0,0:01:00.56,0:01:03.74,Default,,0000,0000,0000,,所以m=-1
Dialogue: 0,0:01:03.94,0:01:09.21,Default,,0000,0000,0000,,但是我们不能确定y截距是多少
Dialogue: 0,0:01:09.21,0:01:11.68,Default,,0000,0000,0000,,我们知道直线方程的形式是
Dialogue: 0,0:01:11.98,0:01:20.37,Default,,0000,0000,0000,,y等于斜率 -1x加b b是y截距
Dialogue: 0,0:01:20.37,0:01:23.56,Default,,0000,0000,0000,,现在 我们可以利用坐标的信息
Dialogue: 0,0:01:23.56,0:01:25.32,Default,,0000,0000,0000,,直线经过这个点
Dialogue: 0,0:01:25.32,0:01:27.84,Default,,0000,0000,0000,,我们可以用这个信息来解出b
Dialogue: 0,0:01:28.55,0:01:31.61,Default,,0000,0000,0000,,直线经过点也就是说
Dialogue: 0,0:01:31.61,0:01:34.23,Default,,0000,0000,0000,,当x=4/5
Dialogue: 0,0:01:34.23,0:01:38.53,Default,,0000,0000,0000,,y=0一定满足这个方程
Dialogue: 0,0:01:38.53,0:01:44.28,Default,,0000,0000,0000,,代入 当x=4/5 y=0
Dialogue: 0,0:01:44.28,0:01:50.16,Default,,0000,0000,0000,,所以0=-1×4/5+b
Dialogue: 0,0:01:50.16,0:01:51.75,Default,,0000,0000,0000,,向下滚动一点
Dialogue: 0,0:01:52.78,0:01:58.05,Default,,0000,0000,0000,,我看一下 0=-4/5+b
Dialogue: 0,0:01:58.05,0:02:01.57,Default,,0000,0000,0000,,方程两边加4/5
Dialogue: 0,0:02:02.00,0:02:04.14,Default,,0000,0000,0000,,这是4/5
Dialogue: 0,0:02:04.14,0:02:06.92,Default,,0000,0000,0000,,这边也要加4/5
Dialogue: 0,0:02:07.43,0:02:09.91,Default,,0000,0000,0000,,我这么做的原因是要消掉这个
Dialogue: 0,0:02:10.00,0:02:12.85,Default,,0000,0000,0000,,就得到b=4/5
Dialogue: 0,0:02:16.02,0:02:18.64,Default,,0000,0000,0000,,这样我们就得到了直线的方程
Dialogue: 0,0:02:19.14,0:02:22.04,Default,,0000,0000,0000,,y等于-1乘x
Dialogue: 0,0:02:22.04,0:02:32.03,Default,,0000,0000,0000,,也可以写成-x 加b 4/5 就像这样
Dialogue: 0,0:02:32.35,0:02:33.92,Default,,0000,0000,0000,,现在看这一题
Dialogue: 0,0:02:34.54,0:02:39.65,Default,,0000,0000,0000,,直线穿过点(2,6)和(5,0)
Dialogue: 0,0:02:39.65,0:02:43.46,Default,,0000,0000,0000,,题目没有明确给我们斜率和y截距
Dialogue: 0,0:02:43.46,0:02:45.79,Default,,0000,0000,0000,,但是我们可以通过坐标把这些求出来
Dialogue: 0,0:02:45.79,0:02:47.94,Default,,0000,0000,0000,,所以首先要做的就是算出斜率
Dialogue: 0,0:02:48.02,0:02:54.95,Default,,0000,0000,0000,,我们知道斜率m等于y变化量除x变化量
Dialogue: 0,0:02:55.25,0:02:57.56,Default,,0000,0000,0000,,也就等于 y变化量是多少？
Dialogue: 0,0:02:58.00,0:02:59.50,Default,,0000,0000,0000,,从这一点开始
Dialogue: 0,0:02:59.50,0:03:05.09,Default,,0000,0000,0000,,这是(6,0) 这样做
Dialogue: 0,0:03:05.09,0:03:10.30,Default,,0000,0000,0000,,这是6 标上颜色 减0
Dialogue: 0,0:03:10.30,0:03:14.01,Default,,0000,0000,0000,,6-0 这就是y变化量
Dialogue: 0,0:03:14.23,0:03:23.39,Default,,0000,0000,0000,,x变化量是2-5
Dialogue: 0,0:03:24.01,0:03:26.24,Default,,0000,0000,0000,,标上颜色是为了给你们展示
Dialogue: 0,0:03:26.24,0:03:30.54,Default,,0000,0000,0000,,当先用这个y 用上面这个6
Dialogue: 0,0:03:30.84,0:03:33.46,Default,,0000,0000,0000,,那我就要先用这个x
Dialogue: 0,0:03:33.46,0:03:36.47,Default,,0000,0000,0000,,我要告诉你们 这是坐标(2,6)
Dialogue: 0,0:03:36.47,0:03:38.72,Default,,0000,0000,0000,,这是坐标(5,0)
Dialogue: 0,0:03:38.72,0:03:41.66,Default,,0000,0000,0000,,2和5不能交换
Dialogue: 0,0:03:41.66,0:03:44.49,Default,,0000,0000,0000,,那样就会得到答案的相反数
Dialogue: 0,0:03:45.00,0:03:46.15,Default,,0000,0000,0000,,但在这里得到什么？
Dialogue: 0,0:03:46.15,0:03:54.61,Default,,0000,0000,0000,,这就是6-0=6 2-5=-3
Dialogue: 0,0:03:54.81,0:03:57.82,Default,,0000,0000,0000,,所以这就变成了-6/3
Dialogue: 0,0:03:57.82,0:04:02.26,Default,,0000,0000,0000,,也就是-2 这就是斜率
Dialogue: 0,0:04:02.26,0:04:04.82,Default,,0000,0000,0000,,到目前为止我们知道直线一定是
Dialogue: 0,0:04:04.82,0:04:09.29,Default,,0000,0000,0000,,y等于斜率 用橙色表示
Dialogue: 0,0:04:09.29,0:04:15.04,Default,,0000,0000,0000,,-2x加y截距
Dialogue: 0,0:04:15.04,0:04:17.82,Default,,0000,0000,0000,,现在就和上一题一样了
Dialogue: 0,0:04:17.82,0:04:20.68,Default,,0000,0000,0000,,我们可以用其中一个点求出b
Dialogue: 0,0:04:20.68,0:04:21.83,Default,,0000,0000,0000,,任意一点
Dialogue: 0,0:04:22.00,0:04:23.84,Default,,0000,0000,0000,,这两个点都在直线上
Dialogue: 0,0:04:23.84,0:04:26.60,Default,,0000,0000,0000,,所以这两点都满足方程
Dialogue: 0,0:04:26.90,0:04:28.56,Default,,0000,0000,0000,,我要用点(5,0)
Dialogue: 0,0:04:28.56,0:04:30.78,Default,,0000,0000,0000,,因为如果有个数是0通常比较好算
Dialogue: 0,0:04:30.98,0:04:32.74,Default,,0000,0000,0000,,运算比较简单
Dialogue: 0,0:04:32.74,0:04:34.56,Default,,0000,0000,0000,,所以把(5,0)代入
Dialogue: 0,0:04:34.56,0:04:38.85,Default,,0000,0000,0000,,当x=5 y=0
Dialogue: 0,0:04:38.85,0:04:43.51,Default,,0000,0000,0000,,当这是-2×5时 y=0
Dialogue: 0,0:04:43.51,0:04:47.25,Default,,0000,0000,0000,,当x=5 再加b
Dialogue: 0,0:04:47.25,0:04:52.29,Default,,0000,0000,0000,,所以得到0=-10+b
Dialogue: 0,0:04:52.59,0:04:55.43,Default,,0000,0000,0000,,如果方程两边加10
Dialogue: 0,0:04:56.37,0:05:00.78,Default,,0000,0000,0000,,如果两边加10 这两个约掉了
Dialogue: 0,0:05:00.78,0:05:04.11,Default,,0000,0000,0000,,就得到b=10+0=10
Dialogue: 0,0:05:04.11,0:05:05.95,Default,,0000,0000,0000,,就得到b=10
Dialogue: 0,0:05:06.04,0:05:08.22,Default,,0000,0000,0000,,现在我们求出了直线的方程
Dialogue: 0,0:05:08.22,0:05:12.03,Default,,0000,0000,0000,,方程是y 用个新颜色
Dialogue: 0,0:05:12.96,0:05:23.58,Default,,0000,0000,0000,,y等于-2x加b 就是加10 做完了
Dialogue: 0,0:05:23.58,0:05:24.88,Default,,0000,0000,0000,,再做一题
Dialogue: 0,0:05:28.01,0:05:31.07,Default,,0000,0000,0000,,好了 直线过点(3,5)
Dialogue: 0,0:05:31.07,0:05:32.66,Default,,0000,0000,0000,,点(3,0)
Dialogue: 0,0:05:32.66,0:05:34.34,Default,,0000,0000,0000,,就像上个问题
Dialogue: 0,0:05:34.34,0:05:40.54,Default,,0000,0000,0000,,从求斜率m开始
Dialogue: 0,0:05:40.54,0:05:44.29,Default,,0000,0000,0000,,斜率就是高度除跨度
Dialogue: 0,0:05:44.29,0:05:48.27,Default,,0000,0000,0000,,也就是y变化量除x变化量
Dialogue: 0,0:05:48.27,0:05:49.80,Default,,0000,0000,0000,,如果你们把这作为家庭作业
Dialogue: 0,0:05:49.80,0:05:50.93,Default,,0000,0000,0000,,就不用写这些
Dialogue: 0,0:05:50.93,0:05:52.75,Default,,0000,0000,0000,,我只是想确定你们理解
Dialogue: 0,0:05:52.75,0:05:54.50,Default,,0000,0000,0000,,这些是相同的
Dialogue: 0,0:05:55.01,0:05:58.07,Default,,0000,0000,0000,,y变化量除x变化量是多少？
Dialogue: 0,0:05:58.47,0:06:02.18,Default,,0000,0000,0000,,这等于 先从这边开始
Dialogue: 0,0:06:02.18,0:06:04.01,Default,,0000,0000,0000,,我想让你们知道可以随便找一个点
Dialogue: 0,0:06:04.01,0:06:14.09,Default,,0000,0000,0000,,像这样 0-5
Dialogue: 0,0:06:14.09,0:06:16.30,Default,,0000,0000,0000,,我先用这个坐标
Dialogue: 0,0:06:16.30,0:06:19.72,Default,,0000,0000,0000,,把这看做是结束点 0-5
Dialogue: 0,0:06:19.72,0:06:21.48,Default,,0000,0000,0000,,记得当我们刚开始学这个
Dialogue: 0,0:06:21.48,0:06:24.31,Default,,0000,0000,0000,,我总是把x当做分子
Dialogue: 0,0:06:24.31,0:06:26.10,Default,,0000,0000,0000,,错 应该用y做分子
Dialogue: 0,0:06:26.10,0:06:27.92,Default,,0000,0000,0000,,这是坐标的第二个数
Dialogue: 0,0:06:28.04,0:06:38.80,Default,,0000,0000,0000,,这应该是除-3-3
Dialogue: 0,0:06:41.02,0:06:43.45,Default,,0000,0000,0000,,这是坐标(-3,0)
Dialogue: 0,0:06:44.43,0:06:48.03,Default,,0000,0000,0000,,这是坐标(3,5) 减去它
Dialogue: 0,0:06:48.03,0:06:49.33,Default,,0000,0000,0000,,得到什么？
Dialogue: 0,0:06:49.33,0:06:53.26,Default,,0000,0000,0000,,这就等于 用个中性的颜色
Dialogue: 0,0:06:54.16,0:06:56.40,Default,,0000,0000,0000,,这就等于分子
Dialogue: 0,0:06:56.40,0:07:01.12,Default,,0000,0000,0000,,-5除-3-3是-6
Dialogue: 0,0:07:02.00,0:07:05.63,Default,,0000,0000,0000,,负号消掉了 就得到5/6
Dialogue: 0,0:07:05.63,0:07:08.19,Default,,0000,0000,0000,,我们已知直线方程的形式是
Dialogue: 0,0:07:15.33,0:07:18.69,Default,,0000,0000,0000,,我们把一个点的坐标代入求b
Dialogue: 0,0:07:18.69,0:07:19.41,Default,,0000,0000,0000,,开始
Dialogue: 0,0:07:19.41,0:07:21.40,Default,,0000,0000,0000,,我通常喜欢用含有0的点
Dialogue: 0,0:07:21.40,0:07:33.40,Default,,0000,0000,0000,,所以当x=-3 y=0 加b
Dialogue: 0,0:07:33.40,0:07:37.67,Default,,0000,0000,0000,,所有我做的就是用-3替换x 用0替换y
Dialogue: 0,0:07:37.67,0:07:40.94,Default,,0000,0000,0000,,我知道可以这么做是因为它在直线上
Dialogue: 0,0:07:40.94,0:07:43.35,Default,,0000,0000,0000,,它肯定满足直线方程
Dialogue: 0,0:07:44.00,0:07:45.40,Default,,0000,0000,0000,,我们来解出b
Dialogue: 0,0:07:45.40,0:07:50.76,Default,,0000,0000,0000,,就得到0等于 如果用-3除3
Dialogue: 0,0:07:50.76,0:07:52.01,Default,,0000,0000,0000,,这就成了1
Dialogue: 0,0:07:52.01,0:07:54.60,Default,,0000,0000,0000,,如果6除3 就得到2
Dialogue: 0,0:07:55.00,0:08:01.99,Default,,0000,0000,0000,,所以它变成了-5/2+b
Dialogue: 0,0:08:02.33,0:08:05.31,Default,,0000,0000,0000,,方程两边加5/2
Dialogue: 0,0:08:05.31,0:08:08.65,Default,,0000,0000,0000,,加5/2 加5/2
Dialogue: 0,0:08:08.65,0:08:12.59,Default,,0000,0000,0000,,我喜欢改变记号以便你们都能熟悉
Dialogue: 0,0:08:12.59,0:08:16.68,Default,,0000,0000,0000,,所以方程变成了5/2等于
Dialogue: 0,0:08:16.68,0:08:21.82,Default,,0000,0000,0000,,这是0 等于b b等于5/2
Dialogue: 0,0:08:22.00,0:08:32.13,Default,,0000,0000,0000,,所以直线的方程是y=5/6x+b
Dialogue: 0,0:08:32.13,0:08:38.63,Default,,0000,0000,0000,,b我们算出来是5/2 加5/2 做完了
Dialogue: 0,0:08:38.63,0:08:42.82,Default,,0000,0000,0000,,再做一题 这有个图
Dialogue: 0,0:08:43.45,0:08:45.34,Default,,0000,0000,0000,,我们来算出这个图的方程
Dialogue: 0,0:08:45.34,0:08:47.09,Default,,0000,0000,0000,,这实际上 在某种水平上 更简单一点
Dialogue: 0,0:08:47.09,0:08:47.84,Default,,0000,0000,0000,,斜率是多少？
Dialogue: 0,0:08:47.84,0:08:53.38,Default,,0000,0000,0000,,斜率就是y变化量除x变化量 我们看一下
Dialogue: 0,0:08:53.38,0:08:57.13,Default,,0000,0000,0000,,当x变化 当x变化了1
Dialogue: 0,0:08:57.43,0:09:00.86,Default,,0000,0000,0000,,这就是x变化量 x变化量是1
Dialogue: 0,0:09:00.86,0:09:03.84,Default,,0000,0000,0000,,我只是要把x变化1 增加1
Dialogue: 0,0:09:04.01,0:09:05.73,Default,,0000,0000,0000,,y变化量是多少？
Dialogue: 0,0:09:06.03,0:09:09.69,Default,,0000,0000,0000,,看起来y恰好变化了4
Dialogue: 0,0:09:10.03,0:09:13.77,Default,,0000,0000,0000,,看起来当△x=1时
Dialogue: 0,0:09:13.77,0:09:20.07,Default,,0000,0000,0000,,△y y变化量等于4
Dialogue: 0,0:09:20.77,0:09:22.39,Default,,0000,0000,0000,,所以y变化量除x变化量
Dialogue: 0,0:09:22.39,0:09:26.32,Default,,0000,0000,0000,,当x变化量是1 y变化量是4
Dialogue: 0,0:09:26.32,0:09:32.20,Default,,0000,0000,0000,,所以斜率是4 现在 y截距是多少？
Dialogue: 0,0:09:32.20,0:09:33.82,Default,,0000,0000,0000,,现在我们看一下图像
Dialogue: 0,0:09:33.82,0:09:38.86,Default,,0000,0000,0000,,看起来它与y轴交于y=-6
Dialogue: 0,0:09:38.86,0:09:41.43,Default,,0000,0000,0000,,或者点(0,-6)
Dialogue: 0,0:09:41.43,0:09:44.25,Default,,0000,0000,0000,,所以我们知道b=-6
Dialogue: 0,0:09:46.69,0:09:49.05,Default,,0000,0000,0000,,所以就求出了直线的方程
Dialogue: 0,0:09:49.05,0:09:51.43,Default,,0000,0000,0000,,直线方程是y等于
Dialogue: 0,0:09:51.43,0:10:01.69,Default,,0000,0000,0000,,斜率乘x加y截距 我可以这么写
Dialogue: 0,0:10:01.99,0:10:05.85,Default,,0000,0000,0000,,-6 就是加-6
Dialogue: 0,0:10:05.85,0:10:09.31,Default,,0000,0000,0000,,所以这就是直线的方程
Dialogue: 0,0:10:09.71,0:10:12.64,Default,,0000,0000,0000,,再做一题
Dialogue: 0,0:10:12.94,0:10:18.70,Default,,0000,0000,0000,,题目说f(1.5)=-3 f(-1)=2
Dialogue: 0,0:10:18.70,0:10:19.78,Default,,0000,0000,0000,,这是什么？
Dialogue: 0,0:10:19.78,0:10:23.81,Default,,0000,0000,0000,,所有这些就是以一种奇特的方式告诉你们
Dialogue: 0,0:10:23.81,0:10:30.18,Default,,0000,0000,0000,,当x=1.5 当把1.5代入函数
Dialogue: 0,0:10:30.18,0:10:32.89,Default,,0000,0000,0000,,函数值就是-3
Dialogue: 0,0:10:33.44,0:10:37.47,Default,,0000,0000,0000,,这就是说点(1.5,3)在直线上
Dialogue: 0,0:10:38.02,0:10:41.39,Default,,0000,0000,0000,,然后题目给了一个点 当x=-1
Dialogue: 0,0:10:44.54,0:10:46.13,Default,,0000,0000,0000,,这只是以一种特别的方式告诉你们
Dialogue: 0,0:10:46.51,0:10:51.31,Default,,0000,0000,0000,,这两个点都在直线上 没啥特别的
Dialogue: 0,0:10:51.31,0:10:53.62,Default,,0000,0000,0000,,我认为这个问题的关键就是
Dialogue: 0,0:10:53.62,0:10:55.34,Default,,0000,0000,0000,,让你们熟悉函数记号
Dialogue: 0,0:10:55.34,0:10:58.15,Default,,0000,0000,0000,,当你们看到这样的东西不会害怕
Dialogue: 0,0:10:58.15,0:11:01.57,Default,,0000,0000,0000,,如果你们让x=1.5 就得到-3
Dialogue: 0,0:11:01.57,0:11:06.04,Default,,0000,0000,0000,,如果设y=f(x) 这就是坐标
Dialogue: 0,0:11:06.04,0:11:07.51,Default,,0000,0000,0000,,所以这是y坐标
Dialogue: 0,0:11:07.51,0:11:09.34,Default,,0000,0000,0000,,当x=1.5 y应该等于-3
Dialogue: 0,0:11:09.34,0:11:10.70,Default,,0000,0000,0000,,不管怎样 我已经说过好多次了
Dialogue: 0,0:11:10.70,0:11:12.50,Default,,0000,0000,0000,,我们来算出直线斜率
Dialogue: 0,0:11:13.02,0:11:19.25,Default,,0000,0000,0000,,斜率就是y变化量除x变化量 等于
Dialogue: 0,0:11:20.00,0:11:27.05,Default,,0000,0000,0000,,2减去这个数 -3
Dialogue: 0,0:11:27.38,0:11:31.34,Default,,0000,0000,0000,,这就是y值 除 所有这些除
Dialogue: 0,0:11:34.17,0:11:40.16,Default,,0000,0000,0000,,-1减去这个数
Dialogue: 0,0:11:40.16,0:11:48.42,Default,,0000,0000,0000,,这样写 -1减这个数 减1.5
Dialogue: 0,0:11:48.42,0:11:50.73,Default,,0000,0000,0000,,我用这个颜色是为了给你们展示一下
Dialogue: 0,0:11:50.73,0:11:52.90,Default,,0000,0000,0000,,-1和2都来源于这个点
Dialogue: 0,0:11:52.90,0:11:57.23,Default,,0000,0000,0000,,这就是为啥这两个在前面 如果先用这些数
Dialogue: 0,0:11:57.23,0:11:59.31,Default,,0000,0000,0000,,我就要把这个x和y放到前面
Dialogue: 0,0:11:59.31,0:12:01.71,Default,,0000,0000,0000,,如果把2放前面 就要把-1放前面
Dialogue: 0,0:12:01.71,0:12:03.14,Default,,0000,0000,0000,,这就是为啥我用颜色区分
Dialogue: 0,0:12:03.44,0:12:08.41,Default,,0000,0000,0000,,所以这就等于2-(-3)
Dialogue: 0,0:12:08.41,0:12:11.84,Default,,0000,0000,0000,,也就是2+3 等于5
Dialogue: 0,0:12:16.54,0:12:20.99,Default,,0000,0000,0000,,-1-1.5是-2.5
Dialogue: 0,0:12:23.58,0:12:27.80,Default,,0000,0000,0000,,5/2.5等于2
Dialogue: 0,0:12:27.80,0:12:30.09,Default,,0000,0000,0000,,所以直线的斜率是-2
Dialogue: 0,0:12:30.12,0:12:31.78,Default,,0000,0000,0000,,实际上 顺便和你们说一下
Dialogue: 0,0:12:31.78,0:12:33.48,Default,,0000,0000,0000,,我用什么顺序都没关系
Dialogue: 0,0:12:33.48,0:12:35.58,Default,,0000,0000,0000,,如果先用这个坐标
Dialogue: 0,0:12:35.58,0:12:36.85,Default,,0000,0000,0000,,那么就要先用这个坐标
Dialogue: 0,0:12:36.85,0:12:37.91,Default,,0000,0000,0000,,换种方式
Dialogue: 0,0:12:38.01,0:12:54.82,Default,,0000,0000,0000,,如果写成-3-2除1.5-(-1)
Dialogue: 0,0:12:54.82,0:13:00.43,Default,,0000,0000,0000,,这就是减2除1.5-(-1)
Dialogue: 0,0:13:03.32,0:13:05.88,Default,,0000,0000,0000,,得到的结果是相同的 等于多少？
Dialogue: 0,0:13:06.01,0:13:12.76,Default,,0000,0000,0000,,-3-2=-5除1.5-(-1)
Dialogue: 0,0:13:12.76,0:13:16.46,Default,,0000,0000,0000,,这就是1.5+1 除2.5
Dialogue: 0,0:13:16.46,0:13:18.66,Default,,0000,0000,0000,,同样的 等于-2
Dialogue: 0,0:13:18.66,0:13:19.51,Default,,0000,0000,0000,,所以我刚给你们展示了
Dialogue: 0,0:13:19.51,0:13:22.22,Default,,0000,0000,0000,,哪个点作为开始点和结束点都是相同的
Dialogue: 0,0:13:22.22,0:13:24.13,Default,,0000,0000,0000,,只要上下一致
Dialogue: 0,0:13:24.13,0:13:26.52,Default,,0000,0000,0000,,如果这是开始的y 这就是开始的x
Dialogue: 0,0:13:26.52,0:13:29.37,Default,,0000,0000,0000,,如果这是结束的y 这就应该是结束的x
Dialogue: 0,0:13:29.37,0:13:31.96,Default,,0000,0000,0000,,但是不管怎样 我们知道斜率是-2
Dialogue: 0,0:13:33.21,0:13:34.99,Default,,0000,0000,0000,,所以我们知道方程是y等于
Dialogue: 0,0:13:34.99,0:13:39.02,Default,,0000,0000,0000,,-2x加y截距
Dialogue: 0,0:13:39.02,0:13:40.87,Default,,0000,0000,0000,,我们用其中一个坐标
Dialogue: 0,0:13:40.87,0:13:42.99,Default,,0000,0000,0000,,我用这个 因为我不想算小数
Dialogue: 0,0:13:43.44,0:13:46.82,Default,,0000,0000,0000,,我们知道y=2
Dialogue: 0,0:13:47.44,0:13:52.56,Default,,0000,0000,0000,,所以x=-1时 y=2
Dialogue: 0,0:13:55.01,0:13:57.01,Default,,0000,0000,0000,,当然还要加b
Dialogue: 0,0:13:57.22,0:14:02.51,Default,,0000,0000,0000,,所以2等于 -2乘-1等于2加b
Dialogue: 0,0:14:02.51,0:14:05.69,Default,,0000,0000,0000,,如果方程两边减2
Dialogue: 0,0:14:08.08,0:14:10.61,Default,,0000,0000,0000,,方程两边减去它
Dialogue: 0,0:14:10.61,0:14:14.41,Default,,0000,0000,0000,,左边就是0 等于b
Dialogue: 0,0:14:14.41,0:14:15.62,Default,,0000,0000,0000,,所以b是0
Dialogue: 0,0:14:15.62,0:14:19.92,Default,,0000,0000,0000,,所以直线方程是y=-2x
Dialogue: 0,0:14:22.00,0:14:23.97,Default,,0000,0000,0000,,实际上 如果你们想写成函数形式
Dialogue: 0,0:14:23.97,0:14:28.32,Default,,0000,0000,0000,,就应该是f(x)=-2x
Dialogue: 0,0:14:28.32,0:14:30.57,Default,,0000,0000,0000,,我假设y=f(x)
Dialogue: 0,0:14:30.57,0:14:34.07,Default,,0000,0000,0000,,但是这确实是个方程 题目没有提到y
Dialogue: 0,0:14:34.07,0:14:37.87,Default,,0000,0000,0000,,所以这里要写成f(x)=2x
Dialogue: 0,0:14:37.87,0:14:42.69,Default,,0000,0000,0000,,每个坐标都是x和f(x)
Dialogue: 0,0:14:46.89,0:14:49.98,Default,,0000,0000,0000,,所以你们可以把斜率的定义看成
Dialogue: 0,0:14:49.98,0:14:53.50,Default,,0000,0000,0000,,f(x)变化量除x变化量
Dialogue: 0,0:14:53.50,0:14:56.77,Default,,0000,0000,0000,,这些就是一个东西相同的看法