surface area and its volume class9 most important questions
Find the curved surface area of a circular area of a right circular cone whose slant height is 10 cm and the radius of the base is 7 cm
curved surface area of cone = πrl
22/7 * 7 * 10
Answer =220
Find the total surface area of a hemisphere of radius 10 cm
total surface area of a hemisphere=3πr2
3*3.14*10*10
Answer = 942
Write 4=5x-3y in the form ax +by +c=0 and find the values of a b and c
ax +by+c =0
5x +(-3y)=4
5x-3y-4=0
a=5
b=-3
c=-4
When a spherical balloon is filled with air, its radius increases from 7cm to 14cm, find the ratio of the area of the balloon in these two cases
curved surface area of sphere = 4πr²
Radius 7cm Radius 14cm
= 4π(r₁)2 = 4π(r₁)2
= 4π(r₁)2/4π(r₂)2
= (r₁)2/(r₂)2
= (r₁/r₂)2
= (7/14)2
= (1/2)2
= (1/4)
= 1:4
The ratio of the sides of a triangular plot is 3:5:7. and its perimeter is 300 m. Find the area of the plot.
Perimeter = 3x+5x+7x
300 = 15x
x = 300/15
x = 20.
a=3x=3×20
= 60m.
b=5x=5×20
= 100m.
c=7x=7×20
= 140m.
s = a+b+c/2
= 60+100+140/2
= 300/2
= 150m.
Area = √s(s-a)(s-b)(s-c)
= √150(150-60)(150-100)(150-140)
= √150×90×50×10
= √30×5×30×3×5×10×10
= 30×5×10√3
= 1500√3
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