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Trigonometry question. Height of a point on a cylinder. Need some help please.

Hello dear TSR people,

I'm a little stuck on the question in the picture below.

I do understand why the expression for the height of the scratch on the cylinder would take the form "30 + 30cos(theta) cm". What I can't figure out though is why would the angle Theta be expressed as 6x/π ? Could someone please clarify this for me?

Thank you in advance for your time and patience,

Pat

IMAG0040.jpg
Original post by DeadManProp

I do understand why the expression for the height of the scratch on the cylinder would take the form "30 + 30cos(theta) cm". What I can't figure out though is why would the angle Theta be expressed as 6x/π ? Could someone please clarify this for me?


You're presumably familiar with the formula for the length of an arc, s=rθs=r\theta, where theta is in radians.

But you want theta in degrees.

So, if theta is in degrees, we must multiply by pi/180 to get it to radians to put in the formula.

Thus x=30×π180θx = 30 \times \frac{\pi}{180}\theta, where theta is in degrees.

And rearrange to make theta the subject.
(edited 6 years ago)
Original post by ghostwalker
You're presumably familiar with the formula for the length of an arc, s=rθs=r\theta, where theta is in radians.

But you want theta in degrees.

So, if theta is in degrees, we must multiply by pi/180 to get it to radians to put in the formula.

Thus x=30×π180θx = 30 \times \frac{\pi}{180}\theta, where theta is in degrees.

And rearrange to make theta the subject.


Ahh, thank you very much! That makes sense now. ;]

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