For part A, if P is the center of that triangle, then PR and PT have the same length; therefore, triangle RPT is isosceles. For part B, by the definition of an incenter...if P is an incenter, then it is the place where all the angle bisectors meet. Therefore, angles SRP and PRT are congruent, as are angles STP and PTR. Since the vertex angle measures 64, then each of the base angles by the isosceles triangle theorem measure 58. Half of 58 makes the base angles within the smaller triangle measure 29. And if both of those measure 29, by the triangle angle-sum theorem, 180-29-29 = 122 And that's the measure of angle RPT. Eek.
The first one is (4) The second one is (-6) I'm not 101% sure but yeah.
Hello!
The formula for circumference is

and the formula for area of a circle is

. Armed with these formulas, we can begin to find the circumferences and areas of the circles.
20.
C =

C =

C =

C = 13(3.14)
C = 40.8
A =

A =

A =

A = 132.7
The circumference of the circle is 40.8 in and the area of the circle is 132.7 in².21.
[Since we are given the diameter for this problem, to find the circumference, we no longer need to multiply the radius by 2 as in

because the diameter is the radius × 2. For

we do need to divide the diameter by 2.]
C =

C = 49.3
A =

A =

A =

A = 193.5
The circumference of the circle is 49.3 in and the area of the circle is 193.5 in².
And that is all there is to it. I hope this helps you! (: