Q36 of 131 Page 226

If the radius of a circle is tripled, the area becomes

Let r be the radius of a circle.

∴ Area of circle = πr²

If radius is tripled, then new radius will be 3r.

∴ Area of new circle = π(3r)²

= 9π²

9 times of original

Hence, the area of a circle becomes 9 times to the original area.

The circumference of a circle whose area is 81πr², is

The area of a square is 100 cm². The circumference (in cm) of the largest circle cut of it is

The area of a semicircle of radius 4r is

Fill in the blanks to make the statements true.

Perimeter of a regular polygon = length of one side × ___________.