已知x=y+3,求代数式:l/4(x-y)的平方 -0.3(x-y)+0.75(x-y)的平方+3/10(x-y)-2(
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已知x=y+3,求代数式:l/4(x-y)的平方 -0.3(x-y)+0.75(x-y)的平方+3/10(x-y)-2(x-y+7)的值(要过程!)
![已知x=y+3,求代数式:l/4(x-y)的平方 -0.3(x-y)+0.75(x-y)的平方+3/10(x-y)-2(](/uploads/image/z/14921091-27-1.jpg?t=%E5%B7%B2%E7%9F%A5x%3Dy%2B3%2C%E6%B1%82%E4%BB%A3%E6%95%B0%E5%BC%8F%3Al%2F4%28x-y%29%E7%9A%84%E5%B9%B3%E6%96%B9+-0.3%28x-y%29%2B0.75%28x-y%29%E7%9A%84%E5%B9%B3%E6%96%B9%2B3%2F10%28x-y%29-2%28)
由题意知:x-y=3
1/4(x-y)²-0.3(x-y)+0.75(x-y)²+3/10(x-y)-2(x-y+7)
=(1/4+0.75)(x-y)²+(3/10-0.3)(x-y)-2(x-y+7)
=(x-y)²-2(x-y)-14
=3²-2×3-13
=-10
1/4(x-y)²-0.3(x-y)+0.75(x-y)²+3/10(x-y)-2(x-y+7)
=(1/4+0.75)(x-y)²+(3/10-0.3)(x-y)-2(x-y+7)
=(x-y)²-2(x-y)-14
=3²-2×3-13
=-10
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