Question

what is an equation that is true for every value

Answer 1

Here's one:
                         (x + 1) (x - 1) = x² - 1

Another one: 
                         x³ / x(x²)  =  1

How about        (x² + 6x - 17)⁰  =  1

Or triggily:        sin²(x) + cos²(x)  =  1