>>11699513The equations look similar to x=rcos? annd y=rsin?. So I'm just gonna assume the application is the same.
First consider a unit circle. There the radius is 1 so we can just do y=sin? and x=cos?.
And that's literally by definition of sine and cosine. sin is defined as the y-value at ? radians, and cosine is defined as the x-value at ? radians, on a unit circle.
Now a unit circle is radius 1 so if it's a different size circle then you have to multiply by the radius (if it's a unit circle you're still technically multiplying by the radius, but multiplying by 1 doesn't change anything)
hence where the r comes in
x=rcos?
y=rsin?
Now your pic seems to be a physics application, where it is using ? instead of ? as the angle, rho instead of r as radius, and r or z instead of y or x
(so the r in my example is different than the r in your example, my r = your rho, my y = your r)
