x^2+xy=12,
xy+y^2=15,
x^2+xy+xy+y^2=12+15
(x+y)^2=27
x^2+xy=12,
xy+y^2=15
x^2-y^2=-3
（x+y)（x-y)=-3这么做对吗对你确定？100%正确！！！好吧，那你帮我看看这几道题 1)(x^2)·(x^3y^2)÷x^12 2)(2a^2y)^3÷(-1/2a^5y^2)(-2ay)3)(m+n)(m-n)[mn-(m+n)^2][(m-n)^2+mn)] 1)(x^2-xy)÷2x2)(1/4a^b-1/3ab^2)÷1/12ab