# Polar Coordinates and Conics, need help bad

1. Apr 18, 2008

### th3plan

Were on the conic section. I need help how to choose the right interval to evaluate the arc lengh. x=5cost-cos5t and y=5sint-sin5t . I dont get how to choose the inverval to evaluate this, can someone pleasse tell me how. I just dont grasp this.

2. Apr 19, 2008

### Schrodinger's Dog

Does this help?

$$= \int_{a}^{b} \sqrt { [x'(t)]^2 + [y'(t)]^2 }\, dt.$$

5 cos(t) - cos(5t) and 5 sin(t)- sin(5t) will no doubt fall within an area between $x\pi \theta$ and $x\pi\theta$ do you know how to work that out? Or how to work out appropriate ranges for cos and sin?

Personally I'd chose something like between 0 and $\pi$... or 0 and $2\pi$

Last edited: Apr 19, 2008
3. Apr 19, 2008

### HallsofIvy

Those parametric equations do NOT give a conic section.

You can, however, cover the figure by letting t go from 0 to $2\pi$

4. Apr 19, 2008

### th3plan

how do i mathematically find the right interval to evaulate it ?

5. Apr 20, 2008

### Schrodinger's Dog

Which range will your shape fall in?

It's between the range of 0 and 360 degrees (or a full circle) right? In that case what is the range/interval in degrees to radians? Couldn't be 0 to 2$\pi$ could it?

$$\text{radians}=\text{degrees}\times\frac{\pi\;\text{radians}}{180}$$

$$\text{degrees}=\text{radians}\times\frac{180}{\pi\;\text{radians}}$$

Last edited: Apr 20, 2008