cos θ = -0.9135 (0 ≤ θ < 2π )
α = 0.41899 radians <-------- i don't understand this step. How did we get alpha to be this here?
Since cos θ is negative, it means θ is in the second and third quadrants.
θ = π - 0.41899 = 2.723 or
θ = π + 0.41899 = 3.561
α = 0.41899 radians <-------- i don't understand this step. How did we get alpha to be this here?
Since cos θ is negative, it means θ is in the second and third quadrants.
θ = π - 0.41899 = 2.723 or
θ = π + 0.41899 = 3.561
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You've got your answer(s). You also have your angle in the right quadrant(s).
Be sure your calculator is in radian mode (not degrees, not grads). Take inverse cos .9135 to get the related angle. Then put the related angle into the right quadrant(s).
I am becoming less confident that "related" angle is the best word choice. Tentatively (to me) it seems that related angle and reference angle are the same thing: the acute (Q1) angle that has the same absolute-value-trig-function. [Maybe reference angle would have been better. Right now I don't think there is a difference between the two.]
Be sure your calculator is in radian mode (not degrees, not grads). Take inverse cos .9135 to get the related angle. Then put the related angle into the right quadrant(s).
I am becoming less confident that "related" angle is the best word choice. Tentatively (to me) it seems that related angle and reference angle are the same thing: the acute (Q1) angle that has the same absolute-value-trig-function. [Maybe reference angle would have been better. Right now I don't think there is a difference between the two.]