Question 475313
Ok so the equation is a complex number in polar form:
{{{z = r*(cos(theta) + j*sin(theta))}}}
where r is the modulus or the magnitude of the distance from origin on complex plane.
To eliminate the imaginary part, multiply by the conjugate.
The conjugate is just the same number with the imaginary part having the opposite sign.
Ex: z = 2 + 3j, conjugate = 2 - 3j
In polar form the conjugate would be {{{r*(cos(theta) - j*sin(theta))}}}
So multiply by the conjugate:
{{{r(cos(theta) + j*sin(theta)) * r(cos(theta) - j*sin(theta))}}} 
={{{r^2(cos^2(theta) + j*sin(theta)*cos(theta)-j*sin(theta)*cos(theta)-j^2*sin^2(theta))}}}
Middle term cancels
={{{r^2(cos^2(theta)-j^2*sin^2(theta))}}}
j^2 = -1
={{{r^2(cos^2(theta)+ sin^2(theta))}}}
trig identity, sin^2 + cos^2 = 1
={{{r^2}}}
Hope that answered your question.