# I need help solving for x

• Jul 8th 2010, 02:11 AM
GameTheory
I need help solving for x
1. I am asked to find the roots of this function:
ln(x^3 + 1) = sin(2x) + 5

I have completely forgotten how to do this as its been awhile since high school Can anyone please help?

• Jul 8th 2010, 02:13 AM
Ackbeet
That one's nasty. I don't know if it's possible to find the root of that analytically. You might have to use a numerical method or hand it off to a computer.
• Jul 8th 2010, 04:06 AM
mr fantastic
Quote:

Originally Posted by GameTheory
1. I am asked to find the roots of this function:
ln(x^3 + 1) = sin(2x) + 5

I have completely forgotten how to do this as its been awhile since high school Can anyone please help?

No doubt there is additional very important information that you decided was not important enough to include. So please post the question exactly as it's worded from wherever you got it from.
• Jul 8th 2010, 08:36 AM
GameTheory
The teacher asked me to find the root. You can use analytically, numerically or graphically. Judging from the posts I am assuming that an analytical way is pretty much impossible and therefore I can just use my graphing calculator.

Thanks for confirming
• Jul 8th 2010, 08:43 AM
Ackbeet
Looks to be about 3 solutions. Make sure you know to what precision you need to find the solutions!
• Jul 8th 2010, 08:49 AM
Also sprach Zarathustra
First you need ask yourself is there any roots?

You can prove the existence of roots by some theorems...

(There 3 roots...)
• Jul 8th 2010, 08:53 AM
Ackbeet
Reply to AsZ: Given that this post is in the pre-calculus forum, I doubt if the Intermediate Value Theorem is required, or even that it is required to prove the existence of roots. Certainly, proving existence isn't a bad idea - it could save loads of time, especially if there aren't any...
• Jul 8th 2010, 01:57 PM
GameTheory
Using my graphing calculator, i was only able to find 2 roots at: x = 4.8431455 and x = 7.2402863. I wonder where you guys are getting this third root from?
• Jul 8th 2010, 02:12 PM
pickslides
How many times did the two functions intersect when you graphed them?
• Jul 8th 2010, 02:14 PM
Also sprach Zarathustra
Between them x=6.66...