5x² - 3xy - 4y² - 11xy - 7x² + 2y²
= -2x² - 2y² -14xy
= -2(x² + y²) -14xy
= -2×7 - 14×(-2)
= -14 + 28
= 14
x^2+y^2=7,xy=-2,求5x^2-3xy-4y^2-11xy-7x^2+2y^2的值
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