# Homework Help: Equations of alternating half circles

1. Jun 15, 2012

### mattveeg

I working on a final project for vector calculus and am stuck on the equation of my line. I have made a 3d model of -sin (sqrt(x^2+y^2) on top of a circle with D 10.3125 the kicker is instead of a sin I made it with connecting half circles with D 47/32. I need help with the formula before I can do all the vector calculus stuff required for my project.

2. Jun 15, 2012

### HallsofIvy

I really have no idea what you are talking about. Do you mean that you graphed z= -sin(sqrt(x^2+ y^2))? And what do you mean by "on top of a circle"? How is your two dimensional circle oriented in the three dimensional model?

3. Jun 15, 2012

### mattveeg

I drew a straight line on a piece of 3/16 thick plastic. I then drew seven half circles with r= 47/64 alternating above and below x. similar to y= -cos(sqrt (x^2)). Then I cut out below the half circles making a blade of sorts. I then filled a baking spring form with plaster of paris and spun the blade creating something similar to z=-cos(sqrt(x^2+y^2)) except that because I used circles it is not a cosine function. I need to find gradient, tangent planes, volume, surface area etc, but can not without the first formula. thanks for your quick reply, Matt

Last edited: Jun 15, 2012