4(x+2)2-9(x-3)2=0

题目

4(x+2)2-9(x-3)2=0
[2(x+2)+3(x-3)][2(x+2)-3(x-3)]=0.这一步是怎么得来的、?
-3-
Thanks、、

答案

(a-b)(a+b)=a^2-ab+ab-b^2=a^2-b^2
原等式：4(x+2)2-9(x-3)2=0
==>[2(x+2)]^2-[3(x-3)]^2=0
==>[2(x+2)+3(x-3)][2(x+2)-3(x-3)]=0