# Math Help - cosine problem

1. ## cosine problem

" cos(x^2+5x+9)

round answer to 4 decimal places. "
Thanks!

2. ## Re: cosine problem

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?

3. ## Re: cosine problem

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'

4. ## Re: cosine problem

Originally Posted by jonathanraxa
Sorry I forgot to mention. I'm trying to solve for 'x'
then it would help to know ...

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

5. ## Re: cosine problem

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

$\cos(x^2+5x+9) = \, ?$
sorry again. It would equal 0

6. ## Re: cosine problem

Originally Posted by jonathanraxa
sorry again. It would equal 0
That means that $x^2+5x+9$ must be an odd multiple of $\frac{\pi}{2}$.

7. ## Re: cosine problem

if ...

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

then ...

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

$k \in \mathbb{Z}$

8. ## 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

9. ## Re: cosine problem

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.