Hi, for polar equations, you usually need r and theta, in this case, I am only given one bit of information, how do I do it?

1) Convert these polar equations to Cartesian:

a] $\displaystyle r = 4$

b] $\displaystyle r = 2cos\theta$

2) Convert from Cartesian to polar:

a] $\displaystyle x^2 + (y - 1)^2 = 1$

b] $\displaystyle y = x + 1$

Thanks for any help :)