008A Sample Final A, Question 17

Question: Compute the following trig ratios: a) $\sec {\frac {3\pi }{4}}$       b) $\tan {\frac {11\pi }{6}}$       c) $\sin(-120)$

Foundations
1) How is secant related to either sine or cosine?
2) What quadrant is each angle in? What is the reference angle for each?	Answer:
1) Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle \sec(x)={\frac {1}{\cos(x)}}}
2) a) Quadrant 2, b) Quadrant 4, c) Quadrant 3. The reference angles are: Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle {\frac {\pi }{4}},{\frac {\pi }{6}}} , and 60 degrees or ${\frac {\pi }{3}}$

Solution:

Final Answer A:

Since Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle \sec(x)={\frac {1}{\cos(x)}}} , and the angle is in quadrant 2, Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle \sec({\frac {3\pi }{4}})={\frac {1}{\cos({\frac {3\pi }{4}})}}={\frac {1}{\frac {-1}{\sqrt {2}}}}=-{\sqrt {2}}}

Final Answer B:
The reference angle is ${\frac {\pi }{6}}$ and is in the fourth quadrant. So tangent will be negative. Since the angle is 30 degees, using the 30-60-90 right triangle, we can conclude that Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle \tan({\frac {11\pi }{6}})=-{\frac {\sqrt {3}}{3}}}

Final Answer C:
Sin(-120) = - sin(120). So you can either compute sin(120) or sin(-120) = sin(240). Since the reference angle is 60 degrees, or ${\frac {\pi }{3}}$, So Failed to parse (Conversion error. Server ("https://wikimedia.org/api/rest_") reported: "Cannot get mml. Server problem."): {\displaystyle sin(-120)={\frac {\sqrt {3}}{2}}}

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