Question

The diameter of a cone is 7cm and its slant height is 16.5cm. then its total surface area is…cm2
​

Answer 1

S O L U T I O N :

$\underline{\bf{Given\::}}$

• Diameter of a cone, (D) = 7 cm
• Slant height of cone, (l) = 16.5 cm

$\underline{\bf{Explanation\::}}$

As we know that formula of the Total surface area of cone;

$\boxed{\bf{T.S.A = \pi rl + \pi r^{2} \: \:(sq.unit)}}$

A/q

Radius of cone, (r) = D/2

Radius of cone, (r) = 7/2 cm

Now,

$\mapsto\tt{T.S.A = \pi rl +\pi r^{2}}$

$\mapsto\tt{T.S.A = \pi r(l+r)}$

$\mapsto\tt{T.S.A = \dfrac{22}{7} \times \dfrac{7}{2} \bigg(16.5+\dfrac{7}{2} \bigg)}$

$\mapsto\tt{T.S.A = \dfrac{154}{14} \bigg(\dfrac{33+7}{2} \bigg)}$

$\mapsto\tt{T.S.A = \dfrac{154}{14} \times \dfrac{40}{2}}$

$\mapsto\tt{T.S.A = \cancel{\dfrac{154}{14}} \times \cancel{\dfrac{40}{2}}}$

$\mapsto\tt{T.S.A = 11 \times 20}$

$\mapsto\bf{T.S.A = 220\:cm^{2}}$

Thus,

The total surface area of a cone will be 220 cm² .