Question

Whatever is the diameter of the circle, if the area of the circle is 78.5cm 2square?

Answer 1

Answer:

31.42 cm approx.

Step-by-step explanation:

\begin{gathered}\text{Let the radius of the circle be r.}\\\\\text{Then. area = } \pi r^2\\\\\text{But, given area = 78.5 cm} ^2\\\\\text{Thus, according to the question,}\\\\pi r^2 = 78.5\\\\\implies \dfrac{22}{7} \times r^2 = \dfrac{785}{10}\\\\\\\implies r^2 = \dfrac{785 \times 7}{10 \times 22}\\\\\\\implies r^2 = 24.977\\\\\implies r = \sqrt{24.977} = \boxed{4.99 \: cm}\end{gathered}

Let the radius of the circle be r.

Then. area = πr

2

But, given area = 78.5 cm

2

Thus, according to the question,

pir

2

=78.5

⟹

7

22

×r

2

=

10

785

⟹r

2

=

10×22

785×7

⟹r

2

=24.977

⟹r=

24.977

=

4.99cm

\begin{gathered}\text{circumference = } 2 \pi r\\\\= 2 \times \dfrac{22}{7} \times 5\\\\\\= 31.42 \: cm \: approx.\end{gathered}

circumference = 2πr

=2×

7

22

×5

=31.42cmapprox.