If cos θ =-1/2 and tan θ > 0, then find the exact value of cscθ.
Question
If cos θ =-1/2 and tan θ > 0, then find the exact value of cscθ.
Solution
To find the exact value of csc θ, we first need to understand what the given conditions tell us about θ.
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cos θ = -1/2: This tells us that θ is in the second or third quadrant (where cosine is negative).
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tan θ > 0: This tells us that θ is in the first or third quadrant (where tangent is positive).
Combining these two pieces of information, we can conclude that θ is in the third quadrant (where both cosine is negative and tangent is positive).
Now, we know that cos θ = adjacent/hypotenuse. Given that cos θ = -1/2, we can consider a right triangle where the adjacent side is -1 and the hypotenuse is 2.
Using the Pythagorean theorem, we can find the opposite side: sqrt(2^2 - (-1)^2) = sqrt(3).
Since θ is in the third quadrant, the opposite side is also negative, so we have -sqrt(3).
The cosecant function is defined as csc θ = hypotenuse/opposite. Substituting the values we found, we get csc θ = 2 / -sqrt(3).
To rationalize the denominator, we multiply the numerator and the denominator by sqrt(3) to get csc θ = -2sqrt(3) / 3.
So, the exact value of csc θ is -2sqrt(3) / 3.
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