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Bangun Ruang Kerucut

2)
S = 30 cm
t = 24 cm
r² = S² - t²
r² = 30² - 24² = 324
r = √324 = 18 cm
a) Luas Selimut = π r S
L = (3,14)(18)(30) = 1.695,60 cm²
b) Luas Pernukaan  = πr(r+s)
LP = (3.14)(18)(18+30) = 56,52(48) =2.712,96 cm²

3) a= 216°, R = 20 cm
a) r kerucut =  216/360 x 20 = 3/5 x 20 =  12 cm
b) S kerucut = Jari jari  lingkaran = 20 cm
tinggi kerucut = t
t² = s² - r²
t² = 20² - 12² = 256
t = √256 = 16 cm
Luas permukaan Kerucut = π r ( r + s)
LP = 3,14 (12)(12 +20) = 37,68 (32) = 1.205,76 cm²

4) r : t : s = 3 : 4 : 5
misal
r = 3a
t = 4a
s = 5a

luas selimut = 423,9
π r s = 423,9
(3,14)(3a)(5a) = 423,9
15 a² = 423,9/ 3,14 = 135
a² = 135/15 = 9
a = 3
a) ukuran kerucut
r = 3a = 3(3)= 9 cm
t = 4a = 4(3) = 12 cm
s = 5a = 5(3) = 15 cm

b) luas permukaan kerucut = π r ( r + s)
LP = 3,14 (9)(9+15) = 28,26 (24) =678,24 cm²

5)
keliling alas = 56,52
2π r = 56,52
2(3,14) r = 56,52
6,28 r = 56,52
r = (56,52)/(6,28) = 9

Luas selimut = 5/3 luas alas
π r S = 5/3 π r²
s = 5/3 r
s = 5/3 (9) = 15

Luas Permukaan = π r ( r + s)
LP=  (3,14)(9) (9+15)
LP = 28,26 (24)
LP = 678,24 cm²