若x^2+y^2=7,xy=-2,求5x^2-3xy-4y^2-11xy-7x^2+2y^2的值_数学解答

若x^2+y^2=7,xy=-2,求5x^2-3xy-4y^2-11xy-7x^2+2y^2的值

人气：260 ℃　时间：2019-08-18 10:49:20

解答

5x² - 3xy - 4y² - 11xy - 7x² + 2y²
= -2x² - 2y² -14xy
= -2(x² + y²) -14xy
= -2×7 - 14×(-2)
= -14 + 28
= 14