Q.The perimeter of a sector of the circle of area $25\pi$ sq.cm is 20 cm. Find the area of the sector.

Step 1: $\pi r^2=25\pi \Rightarrow r=5$ cm.

Step 2: Perimeter of sector $=2r+s=20 \Rightarrow s=20-10=10$ cm. …

Find r from the circle's area, then s from the sector's perimeter (perimet …

• Confusing the sector's perimeter (2r + arc) with just the arc length.
• Using A = ½r²θ and needing to also find θ, when A = ½rs is a faster route …