Question

If $(3x-4)(5x+7)=15x^2-ax-28$, then $a$ is ______.

• A. 1
• B. - 1
• C. - 2
• D. -5

Answer 1

The correct option is B - 1

$(3x-4)(5x+7)=15x^2-ax-28$

$\Rightarrow$$15x^2+21x-20x-28=15x^2-ax-28$
$\Rightarrow$$15x^2+x-28=15x^2-ax-28$
$\Rightarrow$$x=-ax$
$\Rightarrow$$-a=1$
$\Rightarrow$$a=-1$