Question

Answer 1

b) \(\left(6x+5\right)^2-\left(2x+7\right)^2\)

\(=\left(6x+5+2x+7\right)\left(6x+6-2x-7\right)\)

\(=\left(8x+12\right)\left(4x-1\right)\)

\(=4\left(2x+3\right)\left(4x-1\right)\)

Thay x=-1 vào ta có:

\(4\cdot\left(2\cdot-1+3\right)\left(4\cdot-1-1\right)=-20\)

d) \(\left(x+4\right)^2-\left(x-5\right)^2\)

\(=\left(x+4+x-5\right)\left(x+4-x+5\right)\)

\(=9\left(2x-1\right)\)

Thay x=3 vào ta có:

\(9\cdot\left(2\cdot3-1\right)=45\)