Surface Areas & Volumes | Exercise 13.4 | Q2

CBSE Class 9 Maths | NCERT SolutionS to Exercise | Surface Area of sphere

Question 2: Find the surface area of a sphere of diameter:

(i) 14 cm
(ii) 21 cm
(iii) 3.5m


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Explanatory Answer | Exrecise 13.4 Question 2

Part (i): Diameter of the sphere, d = 14 cm

Radius of the sphere, r = \\frac{d}{2}) = \\frac{14}{2}) = 7 cm
Surface area of sphere = 4 × π × r2
Take π = \\frac{22}{7})
Surface area of sphere = 4 × \\frac{22}{7}) × 7 × 7
= 4 × 22 × 7
= 616 cm2


Part (ii): Diameter of the sphere, d = 21 cm

Radius of the sphere, r = \\frac{d}{2}) = \\frac{21}{2}) cm
Surface area of sphere = 4 × π × r2
Take π = \\frac{22}{7})
Surface area of sphere = 4 × \\frac{22}{7}) × \\frac{21}{2}) × \\frac{21}{2})
= 22 × 3 × 21
= 1386 cm2


Part (iii): Diameter of the sphere, d = 3.5 m

Radius of the sphere, r = \\frac{d}{2}) = \\frac{3.5}{2}) m
Surface area of sphere = 4 × π × r2
Take π = \\frac{22}{7})
Surface area of the sphere = 4 × \\frac{22}{7}) × \\frac{3.5}{2}) × \\frac{3.5}{2})
= 22 × 0.5 × 3.5
= 38.5 m2

 


NCERT Solutions for Class 9 Math | Chapter 13 Video Solutions



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