# Archimedes spiral?

• Apr 8th 2011, 01:26 PM
homeylova223
Archimedes spiral?
Can anyone show how to graph which is an Archimedes spiral?

r=3(theta)
How would I graph this
I mean I know theta is the angle So would I say 3 times 30 degrees r is 90?(Giggle)
• Apr 8th 2011, 02:37 PM
HallsofIvy
Quote:

Originally Posted by homeylova223
Can anyone show how to graph which is an Archimedes spiral?

r=3(theta)
How would I graph this
I mean I know theta is the angle So would I say 3 times 30 degrees r is 90?(Giggle)

Normally the Archimede's spiral is given with theta in radians, not degrees. So at theta= 0, you mark the origin, r= 0. At 45 degrees- halfway between the positive x and y axes, $\displaystyle \theta= \pi/4$ and $\displaystyle r= 3\pi/4$. At 90 degrees, along the positive y- axis, $\displaystyle \theta= \pi/2$ and $\displaystyle r= \3\pi/4$, etc. However, using degrees rather than radians would only change the scale, not the shape.
• Apr 8th 2011, 03:31 PM
NOX Andrew
Wouldn't $\displaystyle r = \dfrac{3\pi}{2}$ at $\displaystyle \theta = \dfrac{\pi}{2}$?
• Apr 8th 2011, 03:57 PM
HallsofIvy
Yes, that was what I thought I wrote!
• Apr 8th 2011, 07:46 PM
homeylova223
Hmm the only confusion I am having in that checking the answer in the back of my book r is 5 10 15 20. I mean your answer makes sense I just do not see why r in my book would be 5 10 15 20 in the polar graph?