Thực hiện phép tính: (a) (x−5)^2.

a) \[{\left( {x - 5} \right)^2} = {x^2} - 10x + 25.\]

b) \[\left( {x + 3} \right)\left( {x-3} \right)--5{x^2} = {x^2} - 9 - 5{x^2} = - 4{x^2} - 9\]

c) \[\left( {1 - 4x} \right)\left( {1 + 4x} \right) + 3{x^2} - 1 = 1 - 16{x^2} + 3{x^2} - 1 = - 13{x^2}\]

d) \[{\left( {2x + 1} \right)^2} - \left( {4x - 3} \right)\left( {x + 7} \right)\]

\[ = 4{x^2} + 4x + 1 - 4{x^2} - 28x + 3x + 21 = - 21x + 22\]