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the area of the semicircle can be worked

out using the formula

a equals pi r squared divided by two

basically it's the same formula

as the area of circle

which is a equals pi r squared but

you're just dividing

this answer by two because a semi circle

takes up half the space

of a full circle

so what you need to do is just

substitute the radius

into this formula

so let's look at example one so we have

a semicircle and we've got the diameter

of the semicircle

which is eight centimeters

um so what we need to do first of all is

half this eight centimeters to give us

the radius of the circle

so our radius

is

four centimeters

so this is our value of r which we

substitute into our formula up here

so let's just write the formula down

again so it's pi

r squared divided by two

so if we substitute the radius which is

four centimeters

we get pi

times four squared

divided by two

so all you need to do is

type this on your calculator now

so if we go shift pi

times four squared

divided by two

so we get the answer of 8 pi

that would be the exact answer in terms

of pi but let's write down the answer as

a decimal

so we get

one two 25.13274123

so let's round this off to three

significant figures so that'll be 25.1

and the units will be centimeters

squared

so that's our final answer