4 = 5?

-20 = -20

16 - 36 = 25 - 45

4^2 - 36 = 5^2 - 45

4^2 - 36 + 81/4 = 5^2 - 45 + 81/4 <-- Add 81/4 to both sides

(4 - 9/2)^2 = (5 - 9/2)^2 <-- Completing the square

(4 - 9/2) = (5 - 9/2) <-- Square root both sides

4 = 5

(4 - 9/2) = (5 - 9/2)

Like >>2 said, should be +-(4 - 9/2) = +-(5 - 9/2)