2+2=5 😮😮!!Find the mistake.

Today I am going to share you a peculiar kind of calculation which gives us the result 2+2=5.
We know,

2+2=4
2+2=4-9/2+9/2

2+2=√(4-9/2)^2+9/2

2+2=√(16-36+81/4)+9/2

2+2=√(-20+81/4)+9/2

2+2=√(25-45+81/4)+9/2

2+2=√(5^2-2.5.9/2+81/4)+9/2

2+2=√(5-9/2)^2+9/2

2+2=5-9/2+9/2

2+2=5

There is a mistake in this calculation.Can you find it??

Thank you