运用平方差公式计算,急!
问题描述:
运用平方差公式计算,急!
(1) (2/3x-y)(2/3x+y)
(2)(xy+1)(xy-1)
(3)(2a-3b)(3b+2a)
(4)(-2b-5)乘(2b-5)
答
1) (2/3x-y)(2/3x+y)
=4/9x^2-y^2
(2) (xy+1)(xy-1)=x^2*y^2-1
(3) (2a-3b)(3b+2a) =4a^2-9b^2
(4) (-2b-5)乘(2b-5)=25-4b^2