Question 1033656
The way I teach it is first to write that
sec 225 = 1/cos 225
Then look for the value of cos 225.
The reference angle is 45 degrees.
In the third quadrant, cosine is negative.
Thus cos 225 = -cos 45 = -sqrt(2)/2 which means
sec 225 = {{{-2/sqrt(2) = -sqrt(2)}}}