Question

A right angle triangle with side 3cm and 4cm is revolved around its base 4cm . find the surface area of solid formed

Answer 1

Answer:

Radius of cone so formed = 3cm

Height of cone so formed = 4 cm

it's slant height will be = √4²+3² = 5cm

CSA of cone = πrl

CSA = 3.14*3*5 = 47.1cm²

TSA = CSA + πr² = 47.1 + 3.14*9 = 75.36cm²

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Answer 2

Given,

h=4cm

and lets take r=3cm

and by Pythagoras,

$l^{2}$=$4^{2}$+$3^{2}$

$l^{2}$=16+9

$l^{2}$=25

$l$=$\sqrt{25}$

$l$=5cm

SO,

Volume=1/3π$r^{2}$h

            =$\frac{1}{3}$ x $\frac{22}{7}$ x 3 x 3 x 4

            =$\frac{22}{7}$ x 3 x 4

            =$\frac{22}{7}$ x 12

            =$\frac{264}{7}$

            = 37.71 $cm^{3}$

TSA=πrl + π$r^{2}$

      = $\frac{22}{7}$x3x5 + $\frac{22}{7}$x3x3

      =$\frac{22}{7}$x15 + $\frac{22}{7}$x9

      =$\frac{330+198}{7}$

      =$\frac{528}{7}$

      =75.42 $cm^{2}$

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