The length of the arc BC is 3.5π
An arc is acute out part of a circumference of a circle. The circumference of a circle is the outer body of a circle.
The area of a circle is expressed as;
A = πr²
where r is the radius of the circle.
The whole angle of a circle is 360° , the cut out arc angle is 90°, therefore the length of the arc = 1/4 circumference of circle.
C = 2πr
49π = πr²
r = 7
C = 2 × π × 7
C = 14π
length of BC = 14π/4
= 3.5π