Question

A radius of circle of 10 cm find the radius of another circle having area foir times the area of the first circle

Answer 1

We know that :-

$r_{1} = 10cm$

$\bold{area \: of \: circle = \pi {r}^{2} }$

$area \: of \: {1}^{st} \: circle( a_{1}) = \frac{22}{7} \times {10}^{2}$

$a_{1} = \frac{2200}{7} {cm}^{2}$

Area of second circle is 4 times the area of first, so

$\bold{a_{2} = 4( a_{1})}$

$\frac{22}{7} \times {r}^{2} = 4 \times \frac{2200}{7}$

$( \frac{22}{7} \times \frac{7}{2200} ) {r}^{2} = 4 \\ \\ {r}^{2} = 400$

$r = \sqrt{400}$

$\bold{r = 20cm}$

Therefore, the radius of second circle is 20cm