A complex number a + ib can be written in the polar form r*cis A where r is the absolute value of the complex number or sqrt (a^2 + b^2) and A = arc tan (y/x)
Here we have z = 6 - 4i.
r = sqrt (6^2 + 4^2) = sqrt (36 + 16) = 2*sqrt 13
A = arc tan (-4/6) = arc tan (-2/3) = -33.69 degrees
The polar form of the complex number is 2*sqrt 13 cis -33.69