Solving basic Trigonometric functions for all values.

I've been working on problems with the basic setup: Select one or more expressions that together represent all solutions to the equation. Your answer should be in radians.

For example, Cos(x) = √2/2 

The answer(s) are usually given as +/- pi/4 + 2pi*n (n being an integer)

If you give the answer 7pi/4 + 2pi*n this is usually marked as incorrect. Wouldn't this also be a solution to the equation? Why restrict the answers from -pi to pi?