諗爆頭!!好心人幫幫手解呢條有兩個未知數既方程!!!

(b)
代A(-1,0))入方程y=px2次+qx-2

0 = p(-1)2次 + q(-1) - 2
p - q = 2 ---------(1)

代B(4,0)入方程y=px2次+qx-2

0 = p(4)2次 + q(4) - 2
16p + 4q = 2
8p + 2q = 1 ---------(2)

(2) + (1)x2
10p = 5
p = 1/2

代p = 1/2入(1)
q = p - 2
q = -3/2

b)
先代 ( -1,0 ) 入 y=px2次+qx-2

p(-1)2次+q(-1) - 2 =0
p-q-2= 0 ------------(1)

再代(4,0) 入 y=px2次+qx-2

p(4)2次+q(4) - 2 = 0
16p+4q-2=0
8p+2q-1=0 -------------(2)

(1) , p=2+q ------(3)

代(3) 入(2),

8( 2+q ) +2q-1=0
16+8q+2q-1=0
10q+15=0
10q= -15
q= -3/2

代 q= - 3/2 入 (3) ,

p=2+( -3/2 )
p=2-3/2
p=1/2

∴p=1/2 , q= -3/2