+0  
 
0
894
4
avatar+267 

How would I solve an equation like this? Taking the arcsine of both sides doesn't lead me to anywhere that'd be benefitial.

 

I understand that there's and infinite amount of answers but for example what if I wanted all the solutions between 0 and 2pi? How would I go about solving something like this where I can't seem to pull out an x. 

 

Cheers and thanks in advance.

 Nov 14, 2016

Best Answer 

 #2
avatar+33661 
+11

There are 3 solutions.  One is obvious from the graph below. The other two can be found numerically (one way is to guess, using the graph as a starting point, and then refine your guess until you get as close as you want).

 

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 Nov 14, 2016
 #2
avatar+33661 
+11
Best Answer

There are 3 solutions.  One is obvious from the graph below. The other two can be found numerically (one way is to guess, using the graph as a starting point, and then refine your guess until you get as close as you want).

 

.

Alan Nov 14, 2016
 #3
avatar+267 
0

Silly me I'm not sure why I thought there'd be an infinite amount of solutions. I thought that taking the arcsine would add a period of 360 degrees to the answer I suppose. Thank you. Is there a way to solve this algebraically? And an additional question for sinx = 1 - x/pi. Can I solve that algebraically? I imagine it'd be mire difficult.. 

Quazars  Nov 14, 2016
 #4
avatar+33661 
+6

You cannot obtain an explicit algebraic solution in the form x = something here, where the 'something' is independent of x.

 

A possible numerical approach is to use the Newton-Raphson method, where you have to subtract one side from the other to create a function that is equal to zero:

 

The positive solution here is x = 2.314.  The negative solution could be obtained by using an initial guess of, say -3, though the symmetry here makes it obvious that the negative solution is x = -2.314.

 

You would need to use a similar numerical method for your other suggestion.

Here one obvious solution is x = pi.  Use Newton-Raphson to find the others.  For example:

 

So another solution is x = 0.828 (and because of the sine curve, the final solution is at x = 2pi - 0.828).

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 Nov 15, 2016

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