Using the change in base property, we have
approximately.
The perimeter of a semicircle consists of two parts. (the curve and bottom)
That curve is half the distance around the circle, since it's been split in half.
The distance around a circle, the circumfrence, is equal to 2πr, where r is the radius of that circle. In this case, the circumfrence of the entire circle would be 16π. and so that curve would have a length of just 8π.
Using 3.14 for π, 8π = 8×3.14 = 25.12.
As for the flat part, that is the diameter (distance across) our circle.
The radius is the distance from the center of a circle to its edge, and always has half the length of the diameter. (you can break the diameter down into two radii)
If our radius is 8 meters, our diameter (the flat part of that semicircle) must be 16.
Now we add up the two parts of the perimeter...25.12 + 16 = 41.12.
The same would be the right one
We turn -5,12 into polar coordinates. It's a Pythagorean Triple so
r = 13 Ф=arctan(-12/5) + 180° ( in the second quadrant )
so -5 = 13 cos Ф, 12 = 13 sin Ф
12 sin x - 5 cos x = 6.5
13 sinФ sin x + 13 cos Ф cos x = 6.5
13 cos(x - Ф) = 6.5
cos(x - Ф) = 1/2
cos(x - Ф) = cos 60°
x - Ф = ± 60° + 360° k integer k
x = Ф ± 60° + 360° k
x = 180° + arctan(-12/5) ± 60° + 360° k
That's the exact answer;
x ≈ 180° - 67.38° ± 60° + 360° k
x ≈ 122.62° ± 60° + 360° k
x ≈ { 62.62°, 182.62°} + 360° k, integer k
That's vertex form for a parabola 
and we read off vertex (p,q) as
Answer: Vertex (5,7)
The negative <em>a</em> tells us this is a downward opening parabola (upside down from the usual 
. I remember CUP - Concave Up Positive; here <em>a </em>is negative so not a cup, instead concave <em>down.</em> The same rule applies to second derivatives in calculus so memorize it now and use it later.
Answer: downward
