PSLE OEFGH is part of a circle of radius 10 cm. OEG and OFH are quarter circles. The area of the shaded part OFG is 60 cm
2 and the perimeter of the shaded part OFG is 40 cm. For each of the following, use the calculator value of π to find:
- the area of the figure OEFGH, correct to 1 decimal place,
- the perimeter of the figure OEFGH, correct to 1 decimal place.
(a)
Area of the quarter circle
=
14 x π x 10 x 10
= 25π cm
2 Area of sector OGH
= 25π - 60
Area of figure OEFGH
= 25π + 25π - 60
= 50π - 60
≈ 97.1 cm
2 (Correct to 1 decimal place)
(b)
Length of arc FG
= 40 - 10 - 10
= 20 cm
Length of the arc of the quarter circle
=
14 x 2 x π x 10
= 5π cm
Length of arc GH
= (5π - 10) cm
Perimeter of the figure OEFGH
= 5π + 5π - 10 + 10 + 10
= 10π + 10
≈ 41.4 cm (Correct to 1 decimal place)
Answer(s): (a) 97.1 cm
2; (b) 41.4 cm