15. From a solid cylinder of height 2.8 cm and diameter
4.2 cm, a conical cavity of the same height and
same diameter is hollowed out. Find the total
surface area of the remaining solid.
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Answer:
ans = 554.4cm^2
Step-by-step explanation:
diameter = 4.2 cm
radius=2.1 cm
height = 2.8 cm
slant height =√h^2+r^2
=√(2.8)^2 + (2.1)^2
=√7.84 +4.41
=√12.25
=√3.5 x3.5
= 3.5 cm
total surface area of remaining solid = πrl + 2πrh + πr^2
= πr ( l + 2h+ r )
=22/7 x 21/10 ( 35/10 + 2x 28/10 +21/10 )
=66/10 (35/10 +784/10 +21/10 )
=66/10 (35 +784+21/10)
=66/10 x840/10
=554.4 cm^2
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