F.4 MATHS

圖片參考：https://s.yimg.com/lo/api/res/1.2/ZQit8r6YM3UMER1bF6V.OQ--/YXBwaWQ9dHdhbnN3ZXJzO3E9ODU-/http://i.imgur.com/ZH9B85L.gif

I first talk about it generally.

For a straight line in general form: Ax + By + C = 0

Slope = -A/B
x-intercept = -C/A
y-intercept = -C/B

However, you do not need to worry to recite them. I shall teach you the way to derive the result, which is more important to you.

(1)
For slope, write the equation in the form of y = mx + c, then m is the slope and c is the y-intercept.
Ax + By + C = 0
By = -Ax - C
y = (-A/B)x + (-C/B)
here you can see that slope = -A/B and y-intercept = -C/B

(2)
For x-intercept, put y = 0 in the equation:
Ax + 0 + C = 0
Ax = -C
x = -C/A is the x-intercept.

(3)
For y-intercept (another method), put x = 0 in the equation:
0 + By + C = 0
By = -C
y = -C/B is the y-intercept, which is consistent with the above result from y = mx + c

✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀

Method 1
Therefore, for your question: 4x - my - 3m² = 0
A = 4
B = -m
C = -3m²

Slope = -A/B = 4/m = 2/3 = 4/6
That is m = 6.

y-intercept = -C/B = -3m²/m = -3m = -18.

✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀ ✿ ❀

Method 2 (this is even more natural)
Suppose we do not recite the formulae.
Consider 4x - my - 3m² = 0
my = 4x - 3m²
y = (4/m)x - 3m

Slope = 4/m and y-intercept = -3m

4/m = 2/3 gives m = 6.
y-intercept = -3m = -18.

2014-09-16 11:15:52 補充：
補充問：
為何我用 y = mx + c 計出來不是 -18？

補充答：
那你計到什麼數？

首先確認一下，你是否做到 equation 是：
y = (4/m)x - 3m

然後，4/m = 2/3 得 m = 6
最後 y-intercept = -3m = -18

2014-09-16 11:31:05 補充：
好，不用客氣～

加油！

(◕‿◕✿)

明白了,我會再嘗試,謝謝.

ASK YOUR TEACHER!!!!!!!!!!!!!!