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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
