Question

What is the circumference of a semicircle with a 7cm diameter?

Answer 1

$\boxed{\boxed{\boxed{\boxed{\boxed{\bf\mathsf{18\: cm}}}}}}$

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We know that,

$\textsf{Circumference of Circle} \mathsf{\: = 2\pi r}$

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Now,

If we take a semicircle then, Circumference of circle is halved but a new side is also added to it(diameter).

So, The Circumference of Semicircle is,

$\bf\large\mathsf{\frac{2\pi r}{2} + diameter}$

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Taking $\mathsf{r = \frac{7}{2}}$

Now, Putting the Values in the Formula we get,

$\mathsf{ [2 \times \frac{22}{7} \times \frac{7}{2} ] + 7}$

$=> \mathsf{[11] + 7}\\=> \large\mathsf{18 \: cm}\\\\\textsf{Hence, Circumference of Semi-circle is 18 cm.}$

Answer 2

Diameter = 7 cm (Given)

Find the radius:

Radius = Diameter ÷ 2

Radius = 7 ÷ 2 = 3.5 cm

Find the circumference of the circle:

Circumference of a circle = 2πr

= 2π (3.5) = 22 cm

Find the circumference of the semicircle:

Circumference of Semicircle =  [ Circumference of a circle ÷ 2 ] + Diameter

Circumference of Semicircle =  [ 22 ÷ 2 ] + 7

Circumference of Semicircle = 11 + 7

Circumference of Semicircle = 18 cm

Answer: The circumference of the semicircle is 18 cm