Calculus question

Question

The integral a=-5, b=5, ∫√(25−x^2)dx gives the area of a region R in the xy−plane.

a) Identify and sketch the region R.

b) Find the area of R using a known geometric formula, not by evaluating the

integral.

Answer 1

R is the upper half of a circle centered at (0,0) with radius 4

PI*r^2 is the area of the circle. divide that by 2 (half a circle)

not sure what C means. part b is the exact value of the integral.