已知:x²+xy=12,xy+y²=15,求2x²-2y²的值,
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/01 01:21:34
![已知:x²+xy=12,xy+y²=15,求2x²-2y²的值,](/uploads/image/z/3169739-11-9.jpg?t=%E5%B7%B2%E7%9F%A5%3Ax%26%23178%3B%2Bxy%3D12%2Cxy%2By%26%23178%3B%3D15%2C%E6%B1%822x%26%23178%3B-2y%26%23178%3B%E7%9A%84%E5%80%BC%2C)
已知:x²+xy=12,xy+y²=15,求2x²-2y²的值,
已知:x²+xy=12,xy+y²=15,求2x²-2y²的值,
已知:x²+xy=12,xy+y²=15,求2x²-2y²的值,
两式相减
x²+xy-xy-y²=12-15
x²-y²=-3
2x²-2y²=-6
2x²-2y²
=2(x²-y²)
=2(x²+xy-xy-y²)
=2[(x²+xy)-(xy+y²)]
=2[12-15]
=2×(-3)
= -6