PSLE OCDEF is part of a circle of radius 15 cm. OCE and ODF are quarter circles. The area of the shaded part ODE is 120 cm
2 and the perimeter of the shaded part ODE is 45 cm. For each of the following, use the calculator value of π to find:
- the area of the figure OCDEF, correct to 1 decimal place,
- the perimeter of the figure OCDEF, correct to 1 decimal place.
(a)
Area of the quarter circle
=
14 x π x 15 x 15
= 56.25π cm
2 Area of sector OEF
= 56.25π - 120
Area of figure OCDEF
= 56.25π + 56.25π - 120
= 112.5π - 120
≈ 233.4 cm
2 (Correct to 1 decimal place)
(b)
Length of arc DE
= 45 - 15 - 15
= 15 cm
Length of the arc of the quarter circle
=
14 x 2 x π x 15
= 7.5π cm
Length of arc EF
= (7.5π - 15) cm
Perimeter of the figure OCDEF
= 7.5π + 7.5π - 15 + 15 + 15
= 15π + 15
≈ 62.1 cm (Correct to 1 decimal place)
Answer(s): (a) 233.4 cm
2; (b) 62.1 cm