what is a semicirles permitier if the diameter is 4

The straight edge of the semicircle is 4 units, as this is this the diameter.

The circumference of the full circle is

C = pi*d = pi*4 = 4pi

which is the distance around the full circle (aka circle's perimeter)

So half of this is 4pi/2 = 2pi

Add this onto the straight edge length to get 4+2pi as the exact distance around the entire semicircle. This includes both straight and curved portions.

If you use the approximation pi = 3.14, then 4+2*pi = 4+2*3.14 = 10.28 is the approximate answer. To get a more accurate answer, use more decimal digits in pi.

In summary,

exact answer in terms of pi is  4+2pi units

approximate answer is roughly 10.28 units (using pi = 3.14)

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hope this .. : d

2.83941151 would be the answer you're looking for! : )