The circumference of the circle is actually the perimeter ( length of the boundary ) of the circle . And a part of the circle which lies between two distinct points on the circumference of the circle is called an arc . If the length of the arc is less than half the circumference , it is called minor arc and remaining portion which is more than half of the circle ( but natural ) is called major arc .
When these two points , which make the arc are joined separately to the centre of circle , these arms make angle at the centre . This is called the angle subtended by the arc at the centre of the circle .
There is a beautiful logical relation exists between arc length and the angle , the arc makes ( subtends ) at the centre of the circle . This relation is as under , the wholle circle subtends an angle of 360 degree at the centre . Half the circumference subtendr 360 / 2 ie 180 degree at the centre . The logical relation becomes Arc Length = Circumference × angle in degrees it ( the arc ) subtends at the centre of the circle / 360 degree . So the answer is very simple :- The Arc Length = 36 × 90 / 360 or 9 units ( may be centimetres or metres or inches , feet , yards , etc ) . Which is definitely length of the minor arc . The length of the major arc ( remaining portion of the circumstance ) is 36 - 9 = 27 units . Hence the required answer of the sum is 9 units .