Question

The figure below is a cone whose base radius is 3.5cm and slant height 7cm. The net of the cone is a sector of a circle.

1. Find the angle subtended at the centre of the sector. 
2. Draw the net of the solid. 

Answer 1

1. Surface area of a cone = πrl
   = ²²/₇ × 3.5 × 7
   =77
   Area of a sector =  θ  πr²
                             360
   (^θ/₃₆₀ × ²²/₇ × 7 × 7 =77)
   θ = 77 × 360
           22 × 7
   =180°
2.