3.14*2.5²-3.14*1.5²

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3.14（旁乎漏2.5^2-1.5^2)
=3.14(2.5+1.5)(2.5-1.5)
=3.14X4
=12.56
要点：平方差公运烂式，和乘法分配顷悉律

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3.14*2.5²-3.14*1.5²改举散
=3.14×（2.5²-1.5²）
=3.14×（2.5+1.5）×（2.5-1.5）核氏答知
=3.14×4×1
=12.56

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