Question

Find the areas of circles whose diameters are

(1) 28 cm

(2) 42 cm

(3) 7 cm

(4) 70 cm

Answer 1

(1) r =

=

= 14 cm

A = πr²

A = π × r × r

= × 14 × 14

= 616 cm²

(2) r =

=

= 21 cm

A = πr²

A = π × r × r

= × 21 × 21

= 1386 cm²

(3) r =

=

= 3.5 cm

A = πr²

A = π × r × r

= × 3.5 × 3.5

= 38.5 cm²

(4) r =

=

= 35 cm

A = πr²

A = π × r × r

= × 35 × 35

= 3850 cm²