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

原式=-2x^2-2y^2-3xy-11xy = -2 * 7 - 14 * (-1) = 0