Question

find the product using identy

(2x - 7y) (2x + 8y)​

Answer 1

$\tt {(2x - 7y) \: (2x + 8y)}$

[using identity] ....

( x + a ) (x + b ) = x^2 + x ( a + b ) + ab

$\tt {=(2x - 7y) \: (2x + 8y)}$

$\tt {=( {2x})^{2} + 2x( - 7y + 8y) + ( - 7y \times 8y)}$

$\tt {= {4x}^{2} + 2xy + ({ - 56y})^{2}}$

$\tt {= {4x}^{2} + 2xy - {56y}^{2}}$