x^2+7x-a^2+a+12

问题描述:

x^2+7x-a^2+a+12

原式=(x^2+7x+12.25) - (a^2-a+0.25)
=(x+3.5)^2 - (a-0.5)^2
=(x+3.5+a-0.5)(x+3.5-a+0.5)
=(x+a+3)(x-a+4)