(-42.75)*(-27.36)-(-72.64)*(+42.75)=?后面有个)(+42.75)为什么前面得负请说明原因

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(-42.75)*(-27.36)-(-72.64)*(+42.75)=?后面有个)(+42.75)为什么前面得负请说明原因

原式=(-42.75)×(-27.36)-(-72.64)×(+42.75)
=42.75×27.36-[-(72.64×42.75)]
=42.75×27.36+72.64×42.75
=42.75×27.36+42.75×72.64
=42.75×(27.36+72.64)
=42.75×100
=4275