to find polar curve area

Plot the polar curve r = 3(cos 2 θ) and curve r = 2 on the same graph and find the area of

the portion outside the curve r = 2 and inside r = 3(cos 2 θ)

[Daniel Pollard]

What have you tried so far?

[Raniya]

I've plotted the graph.

[Raniya]

Answer 1

[Bjorn Gustavsson]

The area of a circle-sector is:

Use that for each small sector of your areas, add them up, then change the number of elements in theta and repeat.

[Raniya]

Hello,thank you for replying me.Yes,I did that but shows error.

[Raniya]

Or maybe there's something wrong in my coding,can you help?

[Daniel Pollard]

Copy and paste the error message and the code you used, that makes it much easier to help.

[Raniya]

ok so the last time forgot to copy and this time i cant even plot the graph.

[Daniel Pollard]

"Unrecognized function or variable th" means that you typed in th without telling Matlab what it is. Do you mean to type theta instead?

[Raniya]

yes,theta is what i meant.I'm sorry.Can you please let me know what to do after this?[PS: i'm new :)]

[Bjorn Gustavsson]

I suggest that instead of:

r = 2;
polar(theta,r+zeros(theta))

You create your two radiuses:

r_circ_of_theta = 2*ones(size(theta));

That is for the circle. Then you do the same for the rose-curve (think that's the name of the -curve).

That way you'll have one array for theta and two arrays with the radial distance to the curves at each value of theta.

HTH

[Raniya]

Hello,thank you for reaching out.It actually worked.Can you please help me code the area?Thank you.

[Bjorn Gustavsson]

You appear to be very new to matlab. Therefore I suggest that you work through the on-ramp tutorials/course:on-ramp.

Then have a browse through the demos and the help.

For integration the simplest ways are: trapz and integral.

HTH