Is there a formula for the points that are contained in the main cardioid of the Mandelbrot set?

The boundary of the cardioid is given by,

which I have seen many times although I have never seen what the 't' stands for...

However this just plots the perimeter.

How could I change this to find a formula for every point contained in the cardioid? Would it just be something simple like putting absolute value signs on both sides and changing the = to a

?

Haven't though that through but was the first thought that came to my head however I'm pretty sure it's wrong...