已知x-2y+3=0 求2x²-8xy+8y²=
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已知x-2y+3=0 求2x²-8xy+8y²=
已知x-2y+3=0 求2x²-8xy+8y²=
已知x-2y+3=0 求2x²-8xy+8y²=
由x-2y+3=0得:
x-2y=-3
两边同时乘以√2得:
√2(x-2y)=-3√2
两边平方:2x²-8xy+8y²=18
2(x-2y)^2=18
18
原式=2(x²-4xy+4y²)=2(x-2y)²
已知x-2y+3=0 ∴x-2y=-3
∴原式=2×(-3)²=2×9=18
2(x-2y)²=2*9=18
第一个式子把三移到等式右边:x-2y=-3
所以:
2x²-8xy+8y²
=2(x-2y)²
=2*(-3)²
=2*9
=18
x-2y=-3
2x²-8xy+8y²=2(x-2y)平米=18