a: \(47^2-37^2\)
\(=\left(47-37\right)\left(47+37\right)\)
\(=84\cdot10=840\)
b: \(87^2+73^2-27^2-13^2\)
\(=\left(87^2-13^2\right)+\left(73^2-27^2\right)\)
\(=\left(87-13\right)\left(87+13\right)+\left(73-27\right)\left(73+27\right)\)
\(=74\cdot100+46\cdot100\)
\(=100\left(74+46\right)=120\cdot100=12000\)
c: \(85\cdot12,7+5\cdot3\cdot12,7\)
\(=85\cdot12,7+15\cdot12,7\)
\(=12,7\left(85+15\right)=12,7\cdot100=1270\)
d: \(24^3-64\)
\(=24^3-4^3\)
\(=\left(24-4\right)\left(24^2+24\cdot4+4^2\right)\)
\(=20\cdot688=13760\)
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