# Solving Trig Equations

• Sep 4th 2009, 02:32 PM
Solving Trig Equations
Ok, I have to take an accuplacer, I was doing a practice test online to prepare. I was given the equation:

$\displaystyle \sin(2\theta)+3=4$

I need to find $\displaystyle \theta$

$\displaystyle \sin(2\theta)=1$

When the sine of an angle is equal to one on $\displaystyle [0,2\pi]$ then the angle must be equal to $\displaystyle \frac{\pi}{2}$ right? So I have:

$\displaystyle 2\theta=\frac{\pi}{2}$

$\displaystyle \theta=\pi$

The practice test I as doing is mulitple choice. Of course $\displaystyle \pi$ was actually the wrong answer (Headbang). Where am I going wrong here?
• Sep 4th 2009, 02:47 PM
alexmahone
Quote:

Ok, I have to take an accuplacer, I was doing a practice test online to prepare. I was given the equation:

$\displaystyle \sin(2\theta)+3=4$

I need to find $\displaystyle \theta$

$\displaystyle \sin(2\theta)=1$

When the sine of an angle is equal to one on $\displaystyle [0,2\pi]$ then the angle must be equal to $\displaystyle \frac{\pi}{2}$ right? So I have:

$\displaystyle 2\theta=\frac{\pi}{2}$

$\displaystyle \theta=\frac{\pi}{4}$

Fixed the last statement.
• Sep 4th 2009, 06:12 PM
pacman
You screwed the last line of your solution,

it should be pi/4 not pi
• Sep 5th 2009, 06:34 PM