# cosine problem

• May 8th 2012, 04:38 PM
jonathanraxa
cosine problem
" cos(x^2+5x+9)

round answer to 4 decimal places. "
Thanks!
• May 8th 2012, 05:14 PM
skeeter
Re: cosine problem
Quote:

Originally Posted by jonathanraxa
" cos(x^2+5x+9)

round answer to 4 decimal places. "
Thanks!

what do you want done w/ this expression? directions?
• May 8th 2012, 05:27 PM
jonathanraxa
Re: cosine problem
Quote:

Originally Posted by skeeter
what do you want done w/ this expression? directions?

Sorry I forgot to mention. I'm trying to solve for 'x'
• May 8th 2012, 06:21 PM
skeeter
Re: cosine problem
Quote:

Originally Posted by jonathanraxa
Sorry I forgot to mention. I'm trying to solve for 'x'

then it would help to know ...

$\cos(x^2+5x+9) = \, ?$
• May 8th 2012, 06:23 PM
jonathanraxa
Re: cosine problem
Quote:

Originally Posted by skeeter
then it would help to know ...

$\cos(x^2+5x+9) = \, ?$

sorry again. It would equal 0
• May 8th 2012, 06:31 PM
Plato
Re: cosine problem
Quote:

Originally Posted by jonathanraxa
sorry again. It would equal 0

That means that $x^2+5x+9$ must be an odd multiple of $\frac{\pi}{2}$.
• May 8th 2012, 06:31 PM
skeeter
Re: cosine problem
if ...

$\cos(x^2+5x+9) = 0$

then ...

$x^2 + 5x + 9 = \frac{(2k+1)\pi}{2}$

$k \in \mathbb{Z}$
• May 8th 2012, 10:28 PM
jonathanraxa
Re: cosine problem
Another thing I forgot to mention was that I'm trying to find the smallest positive number 'x' from this equation. I don't know if this helps in any way
• May 9th 2012, 04:20 AM
skeeter
Re: cosine problem
Quote:

Originally Posted by jonathanraxa
Another thing I forgot to mention was that I'm trying to find the smallest positive number 'x' from this equation. I don't know if this helps in any way

Plato and I have laid the groundwork for a solution ... you figure out the specific solution using this last "forgotten" detail.

Next time, try to post the entire problem as written.