Answer: BHere, we have to find total length of semi-circles l
1 , l
2, l
3, .............l
13 with centre A and B alternatively.
Here, r
1 = 0.5cm, r
2= 1 cm, r
3 = 1.5 cm and so on
Circumference = πr
Total length of spiral = πr
1+πr
2+πr
3+......+πr
13=> π(0.5+1+1.5+2+..........) = π*0.5 [1+2+3+4.....+13]
=> 22/7 * 0.5 * 13*14/2 = 11*13 = 143 cm.