PSLE OCDEF is part of a circle of radius 13 cm. OCE and ODF are quarter circles. The area of the shaded part ODE is 104 cm
2 and the perimeter of the shaded part ODE is 39 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 13 x 13
= 42.25π cm
2 Area of sector OEF
= 42.25π - 104
Area of figure OCDEF
= 42.25π + 42.25π - 104
= 84.5π - 104
≈ 161.5 cm
2 (Correct to 1 decimal place)
(b)
Length of arc DE
= 39 - 13 - 13
= 13 cm
Length of the arc of the quarter circle
=
14 x 2 x π x 13
= 6.5π cm
Length of arc EF
= (6.5π - 13) cm
Perimeter of the figure OCDEF
= 6.5π + 6.5π - 13 + 13 + 13
= 13π + 13
≈ 53.8 cm (Correct to 1 decimal place)
Answer(s): (a) 161.5 cm
2; (b) 53.8 cm