How does -2 squared = 2i?

No -2^2 does not equal 2i, the square root of -2 is 2i. This if you are not in algebra 2 yet is because they made up a number that is equal to the square root of -1=i. -2 squared however is just positive 2.

If it is:

(-2)^2 = 4

-(2)^2 = -4