Question

Find the product of $(x+7y)(7x-y)$.

• A. $7x^2+48xy-7y^2$
• B. $7x^2-48xy-7y^2$
• C. $7x^2+48xy+7y^2$
• D. $7x^2-48xy+7y^2$

Answer 1

The correct option is A

$7x^2+48xy-7y^2$

$(x+7y)(7x-y)=x(7x-y)+7y\times (7x-y)$
$=x\times 7x-x\times y+7y\times 7x-7y\times y$

$=7x^2-xy+49xy-7y^2$

$=7x^2+48xy-7y^2$