5x^2-(3x^2+5x^2)+(4y^2+7xy)
=5x^2-3x^2-5x^2+4y^2+7xy
=-3x^2+4y^2+7xy
=-3+16-14
=-1我错了！！ 应该是：先化简再求值5x^2-(3y^2+5x^2)+(4y^2+7xy)其中x=-1y=25x^2-(3y^2+5x^2)+(4y^2+7xy) =5x^2-3y^2-5x^2+4y^2+7xy =y^2+7xy =4-14 =-10