Question

Given that the area $a$ of a circle with radius $r$ and diameter $d$ is $100uni{t}^2$, what is the value of $d^2$?

• A. $\frac{200}{\pi }$
• B. $\frac{300}{\pi }$
• C. $\frac{400}{\pi }$
• D. $\frac{500}{\pi }$

Answer 1

The correct option is C $\frac{400}{\pi }$

$a=\pi r^2$
$100=\pi r^2$
$\Rightarrow r^2=\frac{100}{\pi }$
$\Rightarrow {\left(\frac{d}{2}\right)}^2=\frac{100}{\pi }$
or, $d^2=\frac{400}{\pi }$