Question

(4x + 4)(ax – 1) – x2 +4

In the expression above, a is a constant. If the

expression is equivalent to bx, where b is a constant,

what is the value of b?

A) -5

B) -3

C) 0

D) 12

Answer 1

Answer:

b=-3

Step-by-step explanation:

If the expression simplifies to bx that means the $x^{2}$ terms and the constant terms must be cancel out.

Simplify it first.

$(4x+4)(ax-1)-x^{2} +4\\=(4ax^{2} -4x+4ax-4)-x^{2} +4\\=4ax^{2} -x^{2} -4x+4ax-4+4\\=4ax^{2} -x^{2} -4x+4ax$

We know –4 + 4 will cancel out. If we simplify this expression to only an x term, then the $x^{2}$ terms should be cancelled. Therefore, we say that 4ax^2 – x^2 = 0.

$4ax^{2} -x^{2} =0\\x^{2} (4a-1)=0\\4a-1=0\\4a=1\\a=\frac{1}{4}$

If we put a = ¼, then we can find the value of b:

$=4(\frac{1}{4} )x^{2} -x^{2} -4x+4(\frac{1}{4} )x\\=x^{2} -x^{2} -4x+x\\ (cancel out x^{2} terms)$

$=-3x$

$bx=-3x$      if the  expression is equivalent to bx

Therefore, b = –3.