1. Area of a parallelogram = Base x Height
2. Area of a triangle = 1/2 x Base x Height
3. Area of a trapezium = 1/2 x [Sum of parallel sides] x Height
4. Area of a rhombus = 1/2 x Product of diagonals
(ii) a cube = 6a2
(iii) a cylinder = 2πr(r + h)
(i) cuboid = l x b x h
(ii) cube = l3
(iii) cylinder = πr2h
Note:
I. All angles of a regular polygon have equal degree measures.
II. All sides of a regular polygon are equal in length.
Q1. The length and breadth of a rectangle are 10 cm and 8 cm respectively. Find its perimeter if the length and breadth are (i) doubled (ii) halved.
Ans:
Length of the rectangle = 10 cm
Breadth of the rectangle = 8 cm
(i) When they are doubled,
l = 10 × 2 = 20 cm
and b = 8 × 2 = 16 cm
Perimeter = 2(l + b) = 2(20 + 16) = 2 × 36 = 72 cm
(ii) When they are halved,
l = 10/2 = 5 cm
b = 8/2 = 4 cm
Perimeter = 2(l + b) = 2(5 + 4) = 2 × 9 = 18 cm
Q3. A horse is tethered by a rope 10 m long at a point. Find the area of the region where it can graze (π = 3.14)
Solution: The area of the region the horse can graze is circular with a radius equal to the length of the rope.
The area of the circle is given by πr²
= 3.14 × 10²
= 3.14 × 100
=314
Hence the area of the region the horse can graze is 314 cm².
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