# Homework Help: Forming a series

1. Apr 17, 2010

### CR9

1. The problem statement, all variables and given/known data

3/(2√3)=cos(3t+4.189)

and therefore,

0.866=cos(3t+4.189)

I need to solve for t.

3. The attempt at a solution

I know that cos^(-1)θ has 2 values for every 2 pi, that is at 30 and 330 degrees.

But there is no limit given, so its probably from 0 to infinite,thus the question wants me to form a new series whereby by substituting n=0,1,2,3 and etc, I will be able to find t.

I dont know how to form this new formula/series as I was not thought this chap in calculus 2 (my lecturer was way behiind schedule, hence she skipped it)

Hope you guys can help me.

Thanks alot.

Best regards,

2. Apr 17, 2010

### LCKurtz

Instead of writing 30 and 330, think about 30 and -30 and angles coterminal with those. Using radians like you should in a problem like this you could express those angles as

$$3t + 4.189 = 2n\pi \pm \frac \pi 6,\ n = -\infty..\infty$$

and solve for t. Is that 4.189 what you were really given or just a decimal approximation to it?