Question

If $\sqrt{x-1}-\sqrt{x+1}+1=0$, then $4x$ is equal to ____.

• A. $4\sqrt{-1}$
• B. $0$
• C. $5$
• D. $1\frac{1}{4}$

Answer 1

The correct option is C $5$

We can write it as $\sqrt{x-1}+1=\sqrt{x+1}$

Squaring both sides we get,

$x-1+1+2\sqrt{x-1}=x+1$

$\Rightarrow 2\sqrt{x-1}=1$

Squaring both sides, we get

$4(x-1)=1$

$\therefore 4x=5$