\(a)\) \({\left( {x + 2y} \right)^2}\)\(=x^2+2.x.2y+(2y)^2\)\(= {x^2} + 4xy + 4{y^2}\)
\(b)\) \(\left( {x - 3y} \right)\left( {x + 3y} \right)\) \( = {x^2} - {\left( {3y} \right)^2} = {x^2} - 9{y^2}\)
\(c)\) \({\left( {5 - x} \right)^2}\) \( = {5^2} - 2.5x + {x^2} = 25 - 10x + {x^2}\)
