Question

问已知x²+y²=7，xy=－2，求5x²-3xy-4y²-11xy-7x²+2y²的值

那些&sup都是平方哈，给大家添麻烦了，快一点，今晚要用

Answer 1

x^2+y^2=7,xy=-2
5x^2-3xy-4y^2-11xy-7x^2+2y^2
=-2x^2-14xy-2y^2
=-2(x^2+y^2)-14xy
=-2*7-14*(-2)
=-14+28
=14