Question 431008
Arccosine and cosine are inverses of each other, so {{{arccos(cos(7pi/2))}}} would be equal to {{{7pi/2}}}. However, since the arccosine function restricts the range (since an infinite number of values are obtained), we say that this {{{arccos(cos(7pi/2)) = pi/2}}}. Depending on the context of the problem, either answer could be correct, or even some general answer in the form {{{pi/2 + 2k*pi}}}.