Where sin \theta = \(\frac{opp}{hyp}\) → \(\frac{-3}{5}\) opp = -3, hyp = 5 using pythagoras formula hyp\(^2\) = adj\(^2\) + opp\(^2\) adj\(^2\) = hyp\(^2\) - opp\(^2\) adj\(^2\) = 5\(^2\) - 3\(^2\) → 25 - 9 adj\(^2\) = 16 adj = 4 cos \theta = \(\frac{adj}{hyp}\) → \(\frac{4}{5}\) In third quadrant: cos \theta is negative → - \(\frac{4}{5}\)