Question

Find the product of $(7x-4y)$ 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

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

$(7x-4y)(3x-7y)$

$\Rightarrow$ $7x(3x-7y)-4y(3x-7y)$

$\Rightarrow$ $21x^2-49xy-(12yx-28y^2)$

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

$\Rightarrow 21x^2+28y^2-61xy$