已知x+y=30,x-y=20,求1/5(x-3y)²-12.7的值
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已知x+y=30,x-y=20,求1/5(x-3y)²-12.7的值
x+y=30
x-y=20
解得x=25 y=5
1/5(x-3y)²-12.7
=1/5(25-15)²-12.7
=20-12.7
=7.3
x-y=20
解得x=25 y=5
1/5(x-3y)²-12.7
=1/5(25-15)²-12.7
=20-12.7
=7.3
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