Tan45 = 1, conversely, 1 equals tan45 degrees

Tan45 = 1, conversely, 1 equals tan45 degrees

I don't know what you mean. The equal sign relation is relative, tan45 = 1, which means 1 = tan45. If you mean the inverse trigonometric function, then it is
Arctan1 = 45 ° + 180 ° * k (k is an integer)