Mathematical Problem

1.
[2sqrt(3)]^2 = 12 = 4 + 4 + 4 = 2^2 + 2^2 +2^2
So, angle BAD = angle CBD = 90 degree

2.
(a-1)x^2+2x+1=0 不是一元二次方程
即 a-1 = 0 ...... a=1
方程x^2=b只有一個解 ..... 即 b=0
ax^2+(b+1)x+1/4=0 即是 x^2 + x + 1/4 = 0
(x + 1/2)^2 = 0
x = -1/2

2007-09-02 18:21:07 補充：
呃.....搞亂o左o的次序 ..... 畫返o岩個圖會見到
angle BAD = angle BAC + angle CAD = 45 + 90 = 135 degree