Question

1
what
is the total surface area of a cone having radius and height 21​

Answer 1

GIVEN :–

• Radius of cone = 21 cm

• Height of cone = 21 cm

TO FIND :–

• Total surface area = ?

SOLUTION :–

• We know that –

$\\ \dashrightarrow \large {\boxed{ \bf Total \:\: surface \: \: area =\pi rl + \pi {r}^{2}}}$

• Here –

$\\ \implies\bf l = \sqrt{ {r}^{2} + {h}^{2} }$

$\\ \implies\bf l = \sqrt{ {21}^{2} + {21}^{2}}$

$\\ \implies\bf l = 21 \sqrt{2} \: \: cm$

• Now put the values in formula –

$\\ \implies \bf Total \:\: surface \: \: area =\pi (21)(21 \sqrt{2}) + \pi {(21)}^{2}$

$\\ \implies \bf T.S.A.=\pi (21)^{2} \sqrt{2} + \pi {(21)}^{2}$

$\\ \implies \bf T.S.A.=\pi (21)^{2} \{ \sqrt{2} + 1 \}$

$\\ \implies \bf T.S.A.=\pi (21)^{2} \{1.414+ 1 \}$

$\\ \implies \bf T.S.A.=\pi (21)^{2} (2.414)$

$\\ \implies \bf T.S.A.= \left( \dfrac{22}{7} \right)(21)^{2} (2.414)$

$\\ \implies \bf T.S.A.= \left( \dfrac{22}{7} \right)(441) (2.414)$

$\\ \implies \bf T.S.A.=\dfrac{23420.628}{7}$

$\\ \implies \large{ \boxed{ \bf T.S.A.=3,345.804 \: \: cm ^{2}}}$

Answer 2

Answer:

the t.s.a of cone is 22\7 r (h+r)

Step-by-step explanation:

so the H and R =21

then the 22\7 r (21 )

22* 3

=66 ans