x+2y=8 2y-x=5 则4y²-x²=多少?

问题描述:

x+2y=8 2y-x=5 则4y²-x²=多少?

x+2y=8 2y-x=5
则4y²-x²= (2y+x) (2y-x) = 5x8 = 40

4y²-x²=(2y+x)(2y-x)=8×5=40

4y²-x²=(2y-x)(2y+x)=5*8=40