Discussion

Explanation:

Let the radius of cone be R and radius of sector = r, then the slant height of cone ( l) = r 

Circumference of the sector = Perimeter of base circle of the cone.

∴ 2πR = 2πr × 60/360 

⇒ R = r/6 = 21/6 = 7/2 cm

Total surface area of cone = πr (l + r) = $\frac{22}{7}\times \frac{7}{2}\times \left(21+\frac{7}{2}\right)$ = 269.5 cm²

Hence, option (a).

» Your doubt will be displayed only after approval.