Tolong dong.... Pakai cara... :(

b

luas = 78,5 cm2
r2 = luas / π
= 78,5 / 3,14
= 25 cm
r = √ 25 = 5 cm

1).
a. Luas lingkaran = phi x r²
616 = 22/7 x r²
r² = 616 x 7 : 22
r = √196 = 14 cm
b. Luas lingkaran = phi x r²
78,5 = 3,14 x r²
r² = 78,5 : 3,14
r = √25 = 5 cm
2).
a. Diameter lingkaran = luas lingkaran x 4 : phi
D² = 706,5 x 4 : 3,14
D = √900 = 30 cm
b. Diameter lingkaran = Luas lingkaran x 4/1 : 22/7
D² = 3850 x 4/1 : 22/7
D² = 15400 x 7/22
D² = 107800 : 22
D = √4900
D = 70 cm
3).
a. Diameter² = Luas lingkaran x 4 : phi
D² = 50,24 x 4 : 3,14
D² = √64
D = 8 cm
Keliling = phi x d
Keliling = 3,14 x8 =25,12
b. Diameter² = Luas lingkaran x 4/1 : 22/7
D² = 38,5 x 4/1 : 22/7
D² = 154/1 x 7/22
D² = 1078/22
D = √49 = 7 cm
Keliling = phi x d
Keliling = 22/7 x 7 = 22 cm
4).
Diameter = Luas lingkaran x 4 : phi
D² = 113,04 x 4 : 3,14
D = √144 = 12 cm
Keliling roda = phi x d
Keliling roda = 3,14 x 12
Keliling roda = 37,68 cm
Panjang lintasan roda = 37,68 x 5
Panjang lintasan roda = 188,4 cm = 1,884 meter
5).
D² = 308 x 2/1 x 4/1 x 7/22
D² = 308 x 2 x 4 x 7 : 22
D² = 17248 : 22
D = √784 = 28 cm
Panjang plat besi = phi x d
Panjang plat besi = 22/7 x 28
Panjang plat besi = 88 cm