Find the Exact Value arccos(sec(pi))

Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because secant is negative in the second quadrant.

The exact value of ${\displaystyle \sec \left(0\right)}$ is ${\displaystyle 1}$.

Multiply ${\displaystyle -1}$ by ${\displaystyle 1}$.

The exact value of ${\displaystyle \arccos (-1)}$ is ${\displaystyle \pi }$.