Calc 12!!?

cos(θ) > 0 when θ is in the first quadrant or the fourth quadrant.

cos(θ) = 0.825
θ = cos⁻¹(0.825)
θ = 0.60, 2π - 0.6
θ = 0.60, 5.68

here's a graph, it helps to visualize

arccos(0.825) = 0.6 rad
theta = 0.6, (2pi-0.6)
Just draw cos(x) and answers should makes sense.