已知x+y=-10,xy=16求x²+y²,(x-y)²,(x+2)(y+2),x²-xy+y².求值！
问题描述：
已知x+y=-10,xy=16求x²+y²,(x-y)²,(x+2)(y+2),x²-xy+y².
求值！
答
x^2+y^2=(x+y)^2-2xy=100-2×16
(x-y)^2=(x+y)^2-4xy=100-4×16
x^2-xy+y^2=(x+y)^2-3xy=100-3×16
(x+2)(y+2)=xy+2(x+y)+4=-10+32+4