已知x²+xy=5,xy+y²=-3,代数式3x²+xy-2y²的值?
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![已知x²+xy=5,xy+y²=-3,代数式3x²+xy-2y²的值?](/uploads/image/z/976535-71-5.jpg?t=%E5%B7%B2%E7%9F%A5x%26%23178%3B%2Bxy%3D5%2Cxy%2By%26%23178%3B%3D-3%2C%E4%BB%A3%E6%95%B0%E5%BC%8F3x%26%23178%3B%2Bxy-2y%26%23178%3B%E7%9A%84%E5%80%BC%3F)
已知x²+xy=5,xy+y²=-3,代数式3x²+xy-2y²的值?
已知x²+xy=5,xy+y²=-3,代数式3x²+xy-2y²的值?
已知x²+xy=5,xy+y²=-3,代数式3x²+xy-2y²的值?
x²+xy=5,xy+y²=-3
3x²+xy-2y²
=3(x²+xy)-2xy-2y²
=3(x²+xy)-2(xy+y²)
=3×5-2×(-3)
=21