Question

Salina, Tamara, and Uma are working on their homework together. Salina tells her friends that she got θ=52∘θ=52∘ for the inverse cosine problem she is working on and asks if they got the same answer. Tamara says she got θ=128∘θ=128 ∘ and Uma volunteers her answer of θ=308∘θ=308∘. Is it possible that these are all solutions to the same problem? Justify your answer.

Answer 1

The values reported by Uma, Salina, and Tamara are all possible values for inverse cosine

Explanation:

Solution:-

- The solution to the inverse "cosine" problem would have a general form:

θ = cos^-1 ( a )

Where, a: Any arbitrary constant, - 1 < a < 1

- The value of θ = 52° was reported by Salina suggests that the answer lies in the first quadrant of a cartesian plane where ( sin (θ) , cos (θ) , tan (θ) ) have positive values for "a".

Hence, 0 < a < 1 , θ = 52°

- The value of θ = 128° was reported by Tamara suggests that the answer lies in the second quadrant of a cartesian plane where ( sin (θ) ) have positive values for "a" and (cos (θ) , tan (θ) have negative values for "a". So for cos (128):

Hence, -1 < a < 0 , θ = 128°

- The value of θ = 308° was reported by Uma suggests that the answer lies in the fourth quadrant of a cartesian plane where ( cos (θ) ) have positive values for "a" and (sin (θ) , tan (θ) have negative values for "a". So for cos (308):

Hence, 0 < a < 1 , θ = 308°

- The angle θ reported by Uma and Salina are similar solution because of property law of complementary angles:

cos (θ) = cos ( 360 - θ )

Where, θ = 52°, cos (52°) = cos( 308°) .. Uma and Salina conform

However, cos ( 180 - θ ) = - cos (θ)

cos(128) = - cos ( 52 ) .... Uma and Tamara conform.