\(a)\) \({x^2} - {y^2}\)\(= \left( {x + y} \right)\left( {x - y} \right)\) .
Thay \(x = 87;y = 13\)
Ta có: \({x^2} - {y^2}\)\( = \left( {x + y} \right)\left( {x - y} \right)\)
\( = \left( {87 + 13} \right)\left( {87 - 13} \right)\)\( = 100.74 = 7400\)
\(b)\) \({x^3} - 3{x^2} + 3x – 1\) \( = {\left( {x - 1} \right)^3}\)
Thay \(x = 101\), ta có: \({\left( {x - 1} \right)^3} = {\left( {101 - 1} \right)^3}\)\( = {100^3} = 1000000\)
\(c)\) \({x^3} + 9{x^2} + 27x + 27\) \( = {x^3} + 3.{x^2}.3 + 3.x{.3^2} + {3^3} = {\left( {x + 3} \right)^3}\)
Thay \(x = 97\), ta có:
\({\left( {x + 3} \right)^3} = {\left( {97 + 3} \right)^3}\)\( = {100^3} = 1000000\)
