1. ## Algebra/Trig - HELP!!!!!

Hey,
I have an exam in two days!
And I'm tearing my hair out (and so are all of my friends - I've asked 12 people this question and none of them know how to do it)...

xsin(x)=5
x=

Must use algebraic method for working (not allowed to use graphs).

Thanks,
Bobsalive

2. Originally Posted by bobsalive
Hey,
I have an exam in two days!
And I'm tearing my hair out (and so are all of my friends - I've asked 12 people this question and none of them know how to do it)...

xsin(x)=5
x=

Must use algebraic method for working (not allowed to use graphs).

Thanks,
Bobsalive
I'm not sure what you are talking about. This equation has no solution in terms of elementary functions. If you are allowed Calculus there are a variety of techniques you can use, but if you are denied that the only thing I can really think of is to do a "binary search" for the solution, which amounts to little more than guessing the solution and plugging numbers into a calculator. The method is not algebraic.

-Dan

3. Hey,
We are allowed to use calculus (I think this might be a calculus question - they aren't specifically set out in sections or anything like that).

In terms of the binary search thing, we use a graphical method (using GDCs), and just plugged in y=xsin(x) and y=5 and found the intercepts, which occured at +/- 17.05 (rounded to 4 sf). But we still don't know how to get to this answer via non-graphical means.

Hopefully that helps with trying to answer the question! ANY leads are appreciated =)

Thanks,
Bobsalive

(and just for fun, someone else asked us "xsin(x)=0 x=?")

4. Originally Posted by bobsalive
and just for fun, someone else asked us "xsin(x)=0" x=?
Easy! Anything of which the sine function = 0. X = 0 or 180

Sorry, can't help with the original question. Still thinking about it.

5. Originally Posted by topsquark
is to do a "binary search" for the solution, which amounts to little more than guessing the solution and plugging numbers into a calculator. The method is not algebraic.

-Dan
Hey,
Sorry for misleading people in my first post - it doesn't have to be an algebraic method. It just has to be non-graphical and with working (so you can use calculus or trigonometry or whatever.)

Thanks,
Bobsalive

6. Originally Posted by bobsalive
Hey,
Sorry for misleading people in my first post - it doesn't have to be an algebraic method. It just has to be non-graphical and with working (so you can use calculus or trigonometry or whatever.)

Thanks,
Bobsalive
Try the Newton-Raphson method.

-Dan

7. There's a nice video on the Newton-Raphson method here. It's a link from this great calculus videos site to which the link was posted in "Useful Math Websites" by anyman.