Form 2 數學 ( 圓 )

圓周差:
2(r+3)pie-2rpie
=2rpie+6pie-2rpie
=6pie

Let the radius of the larger circle be x,and therefore the smaller one be (x-3).

Circumference of the larger circle
=2xπ cm

Circumference of the smaller circle
=2(x-3)π
=(2x-6)π cm

The difference in their circumference
=2xπ-(2x-6)π
=(2x-2x+6)π
=6π cm

設兩圓的半徑為r及r+3cm
圓周的差 = 2 * pi * (r+3) - 2 * pi * r cm = 18.85 cm