Question

The circumference of a circle whose area is 81πr2 is ____​

Answer 1

$\underline{\huge\text{Solution}}$

Given :-

Area of a circle =  81πrr²  

$\boxed{\bullet \ \bold{FORMULA \ OF \ AREA \ OF \ CIRCLE = \pi r^{2}}\bullet}$

$\bold{\therefore \pi r^{2} = 81 \pi r^{2}}\\ \bold{\implies r^{2} = 81} \\\bold{\implies r = 9}$

$\boxed{\bold{r = 9}}$

$\boxed{{\bold{\bullet \ FORMULA \ OF \ CIRCUMFERENCE \ OF \ CIRCLE = 2\pi r \ \bullet }}}$

(Putting r = 9)

Circumference = 2πr = 2 × 9 π = 18 π

$\boxed{\bold{Circumference = 18 \pi}}$

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