The Total solution for NCERT class 6-12
Since, AB = BC = CA. So, ABC is an equilateral triangle
Radius = OA = 40 m (Given)
We know, medians of equilateral triangle pass through thecircumcentre and intersect each other at the ratio 2 : 1.
Here AD is the median of equilateral triangle ABC, we can write:
OA/OD = 2/1
or 40/OD = 2/1
or OD = 20 m
Therefore, AD = OA + OD = (40 + 20) m = 60 m
Now, In ΔADC:
By Pythagoras theorem,
AC2 = AD2 + DC2
AC2 = 602 + (AC/2) 2
AC2 = 3600 + AC2 / 4
3/4 AC2 = 3600
AC2 = 4800
or AC = 40√3 m
Therefore, length of string of each phone will be 40√3 m.