Solving sin(x)=x: Need Help with 9th Grade Qwiggle

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In summary, this equation is related to the mathematical function sin, and is only accurate for small values of x. The equation can be expressed in radians, and has a single solution.
  • #1
hyurnat4
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This isn't homework, rather a personal qwiggle that came up when I was in 9th grade and gone down since. The title says it all: [itex]sin(x)=x[/itex], solve for x. I've tried rearranging it all kinds of ways, including taylor series, but I don't seem to get anywhere. Help?
 
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  • #2


Try x=0, Pi, 2Pi, 3Pi, ...
 
  • #3


Draw the graph of y=x and y=sin(x) on the same coordinates and note that the gradient of sin(x) at x=0 is 1, which means that y=x is tangent to sin(x) at x=0.
 
  • #4


A typical example of what we call 'transcendental equation'. The solutions to these equations can only seldom be found exactly, in most cases only approximate numerical solutions are available. Graph intersection shows that the equation x= sin x possesses only one solution for real x and this is simply x=0. This is a very fortunate case.
 
  • #5


Thanks for that. I should have clarified: I wasn't so interested in solving for x as the maths behind it. I've never heard of these transcendental equations before. :Cue three hours of searching wikipedia and wolfram:
 
  • #6


sin(y) -> x for small y(degrees) and if x is expressed in radians. For example,
sin(.5)=.008716535. and .5/(360/2pi)=.008726646

sin(.1)=.001745328 and .1/(360/2pi)=.001745329

etc,etc
 
  • #7


LawrenceC said:
sin(y) -> x for small y(degrees) and if x is expressed in radians. For example,
sin(.5)=.008716535. and .5/(360/2pi)=.008726646

sin(.1)=.001745328 and .1/(360/2pi)=.001745329

etc,etc
More simply, sin(x) is approximately equal to x for x small and in radians. I don't understand why you would want "y(degrees)". I also do not understand what this has to do with the question.
 
  • #8


HallsofIvy said:
... I also do not understand what this has to do with the question.

Just some extra information for the one who posted in case he/she was not aware of it. You obviously consider it a non-sequitur. I don't.
 

1. What does "solving sin(x)=x" mean?

"Solving sin(x)=x" means finding the value or values of x that make the equation true. In other words, it is finding the solution or solutions to the equation.

2. How do I solve sin(x)=x?

There are a few different methods for solving this type of equation, but one common approach is to use a graphing calculator to graph both y=sin(x) and y=x, and then find the points where the two graphs intersect. These points represent the solutions to the equation.

3. What is the significance of the "9th Grade Qwiggle" in the title?

The "9th Grade Qwiggle" in the title refers to the level of math typically covered in 9th grade, and suggests that the question is likely being asked by a 9th grade student. It is also possible that "Qwiggle" is a specific program or curriculum used in the 9th grade math class.

4. Can you explain how to use the Qwiggle method to solve sin(x)=x?

I am not familiar with a specific "Qwiggle method" for solving equations, but as mentioned before, one way to solve this equation is by graphing both y=sin(x) and y=x and finding the points of intersection. Another approach is to use algebraic manipulation to rewrite the equation into a form that can be solved more easily.

5. Are there any tips or tricks for solving equations like sin(x)=x?

One helpful tip is to remember that the solutions to this type of equation will lie on the graph of y=sin(x), which has a repeating pattern with a period of 2π. This can help narrow down the possible solutions and make the problem more manageable. Additionally, it is always a good idea to check your solutions by plugging them back into the original equation to ensure they are correct.

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