Question

如题 已知x不等于y,且x^2-x=13,y^2-y=13,求x+y-7的值

Answer 1

x^2-x=13,y^2-y=13,两式想减得x²-y²-x+y=0即(x-y)(x+y)-(x-y)=0(x-y)(x+y-1)=0因为x不等于y,所以x+y-1=0即x+y=1所以x+y-7=-6