If cosΘ = 0.3, it is implied that cosΘ = 0.3/1
Thus, using Pythagoras' Theorem, we know that the opposite side to the angle, Θ, is √(1 - (0.3)²) = √0.91 = 0.953939201....
Thus, sinΘ ≈ 0.954 (3 dp), which, I think, is approximated to 0.98 according to the solutions.
