Chapter 20. Perimeters and Area of Plane Figures
Chapter 20. Perimeters and Area of Plane Figures
Chapter 20. Perimeters and Area of Plane Figures
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MODULE - 4<br />
Mensuration<br />
22 θ<br />
or 6 22<br />
7<br />
× × o<br />
180<br />
=<br />
<strong>Perimeters</strong> <strong>and</strong> <strong>Area</strong>s <strong>of</strong> <strong>Plane</strong> <strong>Figures</strong><br />
Notes<br />
or<br />
o<br />
180 × 7<br />
θ = = 210<br />
6<br />
o<br />
2<br />
πr θ<br />
So, area <strong>of</strong> the sector =<br />
o<br />
360<br />
22 36×<br />
210<br />
×<br />
7 360<br />
=<br />
o<br />
o<br />
= 66 cm 2<br />
Alternate method for area:<br />
Circumference <strong>of</strong> the circle<br />
= 2πr<br />
22<br />
= 2 × × 6 cm<br />
7<br />
22<br />
<strong>and</strong> area <strong>of</strong> the circle = πr 2 = × 6×<br />
6 cm<br />
7<br />
2<br />
22<br />
22<br />
For length 2 × × 6 cm, area = × 6×<br />
6 cm<br />
7<br />
7<br />
2<br />
So, for length 22 cm, area =<br />
22 6×<br />
6×<br />
7×<br />
22<br />
× cm<br />
7 2×<br />
22×<br />
6<br />
2<br />
= 66 cm 2<br />
CHECK YOUR PROGRESS <strong>20.</strong>5<br />
1. Find the perimeter <strong>and</strong> area <strong>of</strong> the sector <strong>of</strong> a circle <strong>of</strong> radius 14 cm <strong>and</strong> central angle<br />
30 o .<br />
2. Find the perimeter <strong>and</strong> area <strong>of</strong> the sector <strong>of</strong> a circle <strong>of</strong> radius 6 cm <strong>and</strong> length <strong>of</strong> the<br />
arc as 11 cm.<br />
470<br />
Mathematics Secondary Course
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