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Ira Lisetskai [31]
3 years ago
13

Given that sin θ ≈ −0.866, where π < θ < 3 , 2 π find cos θ.

Mathematics
1 answer:
nalin [4]3 years ago
4 0

Answer:

\cos( \theta)  = - 0.5

Step-by-step explanation:

It was given that sin θ ≈ −0.866.

To find cosθ, we apply the Pythagorean property;

\cos^{2} ( \theta) +  \sin^{2} ( \theta) = 1

\implies \cos^{2} ( \theta)  = 1 -  \sin^{2} ( \theta)

We substitute the given value to get:

\cos^{2} ( \theta)  = 1 -(0.866)^{2}

\cos^{2} ( \theta)  = 0.250

Take square root of both sides:

\cos( \theta)  = \pm \sqrt{0.250}

\cos( \theta)  = \pm0.5

But we were given that:

\pi \leqslant  \theta \:  \leqslant  \frac{3 \pi}{2}

which is the third quadrant and we know the cosine function is negative in this quadrant.

Hence

\cos( \theta)= - 0.5

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