Q. 9 H5.0( 1 Vote )

# If the radii of a frustum of a cone are 7 cm and 3 cm and the height is 3 cm, then the curved surface area is …………cm^{2}.

A. 50π

B. 25π

C. 35π

D. 63π

Answer :

In frustum

(Slant height)^{2} = (difference in radii )^{2} + (height)^{2}

(Slant height)^{2} = (R - r)^{2} + (height)^{2}

(Slant height)^{2} = (7cm – 3cm)^{2} + (3 cm)^{2}

(Slant height)^{2} = 16 cm^{2} + 9 cm^{2}

(Slant height)^{2} = 25 cm^{2}

Slant height = √ (25 cm^{2})

Slant height = 5 cm

CSA of frustum = π[R + r]l

= π[7cm + 3cm] × 5cm

= 50 π cm^{2}

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If the radii of a frustum of a cone are 7 cm and 3 cm and the height is 3 cm, then the curved surface area is …………cm^{2}.