(x+y)^2=11,(x-y)^2=7,求xy的值

问题描述:

(x+y)^2=11,(x-y)^2=7,求xy的值

∵(X+Y)=X+2XY+Y=11 (X-Y)=X-2XY+Y=7 ∴(X+Y)-(X-Y)=4XY=11-7=4 ∴XY=1