# Algebraic Trigonometry

• Jun 3rd 2013, 06:33 PM
leuge121
Algebraic Trigonometry
How do you obtain an answer in radians from a special triangle? For example how would you get the answer for this question? (The answer is written but I don't know how to get it). So far I have used the CAST method so I know it is in quadrants 3 and 4. I also know that it is a 30 degree triangle.

sinx= -1/2 Domain: 0<x<2(pi)
x=7(pi)/6, 11(pi)/6

Thanks
• Jun 3rd 2013, 07:15 PM
Prove It
Re: Algebraic Trigonometry
If you know your special triangles, you can convert angles to radians using the fact that $\displaystyle 360^{\circ} = 2\pi ^{C} \implies 1^{\circ} = \frac{\pi}{180}^{C}$.
• Jun 3rd 2013, 07:39 PM
leuge121
Re: Algebraic Trigonometry
How would you do it using the unit circle?
• Jun 3rd 2013, 07:50 PM
Prove It
Re: Algebraic Trigonometry
Once you know the first quadrant's angle \displaystyle \begin{align*} \theta \end{align*}, then the angle in Q2 is \displaystyle \begin{align*} \pi - \theta \end{align*}, the angle in Q3 is \displaystyle \begin{align*} \pi + \theta \end{align*} and the angle in Q4 is \displaystyle \begin{align*} 2\pi - \theta \end{align*}.
• Jun 3rd 2013, 07:51 PM
leuge121
Re: Algebraic Trigonometry
Ahh ok thanks mate.