已知(x+y)²=8,(x-y)²=5,求4xy与x²+y²的值.

问题描述:

已知(x+y)²=8,(x-y)²=5,求4xy与x²+y²的值.

x+y)²-(x-y)²=8-5x²+2xy+y²-x²+2xy-y²=34xy=3xy=3/4(x+y)²-(x-y)²=8+5x²+2xy+y²+x²-2xy+y²=132x²+2y²=13x²+y²=6.5