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Area and Perimeter of a Semicircle

Here we will discuss about the area and perimeter of a semicircle with some example problems.

Area and Perimeter of a Semicircle

Area of a semicircle = 12 πr2

Perimeter of a semicircle = (π + 2)r

Solved example problems on finding the area and perimeter of a semicircle:

1. Find the area and perimeter of a semicircle of radius 7 cm. (Use π = 227).

Solution:

Given, radius = r = 7 cm.

Problems on Area and Perimeter of a Semicircle

Then, area of semicircle = 12 πr2

                                   = 12 × 227 × 72 cm2

                                   = 11 × 7 cm2

                                   = 77 cm2

Perimeter of a semicircle = (π + 2)r

                                     = (227 + 2) × 7 cm

                                     = 367 × 7 cm

                                     = 36 cm


2. Find the area and perimeter of the figure in which PQRS is a square of side 28 cm and STR is a semicircle. (Use π = 227).

Area and Perimeter of Semicircular Figure

Solution:

The required area = Area of the square PQRS + Area of the semicircle STR

                          = a2 + 12 πr2

                          = 282 cm2 + 12 × π × (12 × 28)2 cm2

                          = (282 + 12 × 227 × 142) cm2

                          = (282 + 12 × 227 × 14 × 14) cm2

                          = (282 + 11 × 2 × 14) cm2

                          = (282 + 11 × 28) cm2

                          = 28(28 + 11) cm2

                          = 28 × 39 cm2

                          = 1092 cm2

The required perimeter = PQ + PS + QR + semicircular arc STR

                                  = 28 cm + 28 cm + 28 cm + π × (12 SR)

                                  = 84 cm + 227 × 12 × 28 cm

                                  = 84 cm + 11 × 4 cm

                                  = 84 cm + 44 cm

                                  = 128 cm




9th Grade Math

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