Question

two concentric circle have thier areas in ratio 4:9 and radous is 7cm find diameter of outer circle​

Answer 1

Solution

for two circles of radii r1 and r2

$\frac{a1}{a2} = \frac{\pi \: (r1) {}^{2} }{\pi \: (r2) {}^{2} } \\ = > \frac{4}{9} = ( \frac{r1}{r2} ) {}^{2} \\ = > \frac{r1}{r2} = \frac{2}{3}$

now...

r2=3r1/2

=>r2=1.5(7)

=>d2=2r2=3(7)=21 cm