Question

已知多项式A=x²-x=b,B=x²-ax+3,且A-B=x+2,求a,b的值

Answer 1

a(x^3 - x^2 - 3x) + b(2x^2 + x) + x^3 - 5

= (a+1)x^3 + (2b-a)x^2 + (b-3a)x - 5.

a + 1 = 0,a = -1.

2次多项式化为,

(2b+1)x^2 + (b+3)x - 5,

25 = (2b+1)4 + (b+3)2 - 5,

10b = 20,

b = 2,

2次多项式化为,

5x^2 + 5x - 5

x = -2时,该多项式的值 = 5*4 + 5(-2) - 5 = 5