Question -
Answer -
Given,
Base diameter of cone (d1)= 20 cm
So the radius (r1) = 20/2cm = 10 cm
Top diameter ofCone (d2) = 12 cm
So, the radius (r2) = 12/2cm = 6 cm
Height of the cone (h)= 3 cm
Volume of the frustumof a right circular cone = 1/3 π(r22 + r12 +r1 r2 )h
= π/3(102 +62 + 10 × 6)3
= 616 cm3
Let ‘L’ be the slantheight of cone, then we know that
L = √(r1 –r21)2 + h2
L = √(10 – 6)2 +32
L = √(16 + 9)
L = 5cm
So, the slant heightof cone (L) = 5 cm
Thus,
Total surface area ofthe frustum = π(r1 + r2) x L + π r12 +π r22
= π(10 + 6) × 5 +π × 102 + π × 62
= π(80 + 100 +36)
= π(216)
= 678.85 cm2