中二maths請各位幫幫忙(有4題10分)

(x+7)(x-2)≡x^2+(B-3A)x-B
x^2+5x-14≡x^2+(B-3A)x-B
B = 14 .
B - 3A = 5
14 - 3A = 5
3A = 9
A = 3.

1／8m^2-1／12m
= 1/24m( 3m - 2 ) .

180(n-2)/n = 156
180n - 360 = 156n
24n = 360
n = 15
所以該多邊形的邊數為 15 .

設外角為x, 內角為y.
y + x = 180 及 y - x = 135
解此聯立方程, 得
x = 22.5 及 y = 157.5
180(n-2)/n = 157.5
180n - 360 = 157.5n
22.5n = 360
n = 16
所以該多邊形的邊數為 16 .