experts this is urgent can you please answer my following Q fast

how AD²= 900+1/4 AD²BECOMES

3/4AD²= 900 IN CHAPTER CIRCLES EXERCICE 10.4 QUESTION6

its very urgent please

Question 6:

A circular park of radius 20 m is situated in a colony. Three boys Ankur, Syed and David are sitting at equal distance on its boundary each having a toy telephone in his hands to talk each other. Find the length of the string of each phone.

It is given that AS = SD = DA

Therefore, ΔASD is an equilateral triangle.

OA (radius) = 20 m

Medians of equilateral triangle pass through the circum centre (O) of the equilateral triangle ASD. We also know that medians intersect each other in the ratio 2: 1. As AB is the median of equilateral triangle ASD, we can write

∴ AB = OA + OB = (20 + 10) m = 30 m

In ΔABD,

AD²= AB²+ BD²

AD²= (30)²+

Therefore, the length of the string of each phone will bem.