A helix is a three dimensional spiral. The coiled strands of DNA and the edges of twisted crepe paper are examples of helixes. In the diagram, the y-coordinate of each edge illustrates a cosine function. Write an equation for the y-coordinate of one edge.

Question

A helix is a three dimensional spiral.  The coiled strands of DNA and the edges of twisted crepe paper are examples of helixes.  In the diagram, the y-coordinate of each edge illustrates a cosine function.  Write an equation for the y-coordinate of one edge.

anonymous · Answer

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anonymous · Answer

You want to find a function of the form $y=a\cos(bx)$.

$|a|$ would be the amplitude, and $b$ determines the period of the function. The period of such a function is given by $\dfrac{2\pi}{b}$.

From the picture, you can gather that $a=1$ and that the period is 24.
|dw:1402543783987:dw|
So, you have
$$\frac{2\pi}{b}=24~~\iff~~b=\frac{\pi}{12}$$
The function would be $y=\cos\dfrac{\pi x}{12}$.