9514 1404 393
Answer:
(a) P = 44 cm + 18 cm + 18 cm = 80 cm
(b) 396 cm²
(c) (i) see attached: radius = 7 cm; height ≈ 16.58 cm; slant height = 18 cm
(c) (ii) 7 cm
Explanation:
(a) The length of arc PQR is given by the formula ...
s = rθ . . . . . where r is the radius and θ is the angle in radians
The angle θ in radians is (140°)(π/180°) = (140)(22/7)/(180) = 22/9
So, the arc length is ...
PQR = (18 cm)(22/9) = 44 cm
Then the perimeter of the figure is ...
P = PQR +RO +OP = 44 cm + 18 cm + 18 cm
P = 80 cm
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(b) The area of a sector is given by ...
A = 1/2r²θ = 1/2(rs)
A = (1/2)(18 cm)(44 cm) = 396 cm² . . . area of the sector
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(c) (i) A drawing of the cone is attached. The "slant height" is 18 cm. The radius is found in part (ii) as 7 cm. The height is given by the Pythagorean theorem:
height = √((slant height)² - radius²) = √(18² -7²) = √275
height ≈ 16.58 . . . cm
(ii) The length of arc PQR is the circumference of the base of the cone, given by ...
C = 2πr . . . . where r is the radius of the base of the cone
Filling in the known values, we find ...
44 cm = 2(22/7)r
(44 cm)(7/44) = r = 7 cm . . . . . multiply by 7/44 to find r
The radius of the base of the cone is 7 cm.