Question

Find the area and the perimeter of the shaded regions below. Give your answer as a completely simplified exact value in terms of π (no approximations). The figures below are based on semicircles or quarter circles and problems b), c), and d) are involving portions of a square.

Answer 1

The area of the shaded region = (36·π - 72) cm²

The perimeter of the shaded region = (6·π + 12·√2) cm

Explanation:

The given figure is a sector of a circle and a segment of the circle is shaded

We have that since the arc AC subtends an angle 90° at the center of the circle, the sector is a quarter of a circle, which gives;

Area of sector = 1/4×π×r²

As seen the radius, r = AB = 12 cm

∴ Area of sector = 1/4×π×12² = 36·π cm²

The area of the segment AB = Area of sector ABC - Area of ΔABC

Area of ΔABC = 1/2×Base ×Height =

Since the base and the height = The radius of the circle = 12 cm, we have;

Area of ΔABC = 1/2×12×12 = 72 cm²

The area of the segment AB = 36·π cm² - 72 cm² = (36·π - 72) cm²

The area of the shaded region = The area of the segment AB = (36·π - 72) cm²

The perimeter of the shaded region = 1/4 perimeter of the circle with radius r + Line Segment AC

The perimeter of the shaded region = 1/4 × π × 2 × r + √(12² + 12²) = 1/4 × π × 2 × 12 + 12·√2 = (6·π + 12·√2) cm