What's Wrong in this Proof

Just see this Mathematical proof of 2 = 3….
It is given by the greatest mathematician of India Sreenivas Ramanujam in one of his books..

• -6 = -6
• -10 + 4 = -15 + 9
• Add 25/4 on both the sides…
• -10 + 4 +25/4 = -15 + 9 + 25/4
• square(2 - 5/2)= square(3-5/2)
• 2 - 5/2 = 3 - 5/2 (Cancel 5/2 on both sides),then
• 2 = 3

If possible find what is wrong in this proof…..