已知x^2+y^2=7,xy=-1,求代数式：5x^2-(3xy+4y^2)-(11xy-2y^2)-7x^2
问题描述：
已知x^2+y^2=7,xy=-1,求代数式：5x^2-(3xy+4y^2)-(11xy-2y^2)-7x^2
答
=5x^2-3xy-4y^2-11xy+2y^2-7x^2
=-2x^2-14xy-2y^2
=-2(x^2+y^2)-14xy
=-2*7-14*(-1)
=0
答
=5x²-3xy-4y²-11xy=2y²-7x²
=-2x²-14xy-2y²
=-2(x²+7xy+y²）
=-2(x²+y²+7xy)
=-2(7-7)
=-2乘0
=0
答
5x^2-(3xy+4y^2)-(11xy-2y^2)-7x^2
=5x^2-3xy-4y^2-11xy+2y^2-7x^2
=-2x^2-2y^2-14xy
=-2(x^2+y^2)-14*xy
=-2*7-14*(-1)
=-14+14
=0