Question

$\text{Find the product of}(7x-4y)\text{and}(3x-7y).$

• A. $21x^2$ + $28y^2$ + $61xy$
• B. $21x^2$ - $28y^2$ - $61xy$
• C. $21x^2$ + $28y^2$ - $61xy$
• D. $21x^2$ + $28y^2$ - $37xy$

Answer 1

The correct option is C $21x^2$ + $28y^2$ - $61xy$

$(7x-4y)(3x-7y)$
$=(7x\times 3x)+(7x\times (-7y\left)\right)+\left(\right(-4y)\times (3x\left)\right)+\left(\right(-4y)\times (-7y\left)\right)$

$=21x^2-49xy-12xy+28y^2$

$=21x^2$ + $28y^2-61xy$