Question

（x-y/3)^2-(x+y/3)^2 因式分解

Answer 1

(x-y/3)²-(x+y/3)²=(x-y/3-x-y/3)(x-y/3+x+y/3)=-2y/3*2x=-4xy/3

(x+y)²=18====>x²+y²+2xy=18(1)

(x-y)²=6=====>x²+y²-2xy=6(2)

(1)+(2)

2(x²+y²)=24

x²+y²=12

(1)-(2)

4xy=12

xy=3