Question

(x+1)(x-4)-6=x^2-3x-4-6=x^2-3x-10=(x+2)(x-5)中x^2-3x-10怎么弄成(x

Answer 1

实在理解不了可以这样来解释:

x^2-3x-10=x^2-3x+(9/4)-(49/4) (配方:在二次项系数为1的前提下,常数项配成是一次项系数一半的平方)

=[x-(3/2)]^2-(7/2)^2

=[x-(3/2)+(7/2)][x-(3/2)-(7/2)]

=(x+2)(x-5).