Thực hiện phép tính: a) (6x - 7)(7x - 1) ; b) (4x - 1)^2 + (2x - 5)(2x + 5) ; c)

a) 6x−77x−1

=42x2−6x−49x+7

=42x2−55x+7

b) 4x−12+2x−52x+5

=16x2−8x+1+4x2−25

=20x2−8x−24

c) x+5x+xx−5+25x2−5x

= x + 5x + xx - 5 + 25x(x - 5)

=x+5x−5xx−5+x2xx−5+25x(x−5)

=x2−25+x2+25x(x−5) =2x2xx−5=2xx−5