Convert from polar form to rectangular form r 7cospheta 3s

Solution

We know that
x = rcosØ or cosØ = x/r
y = rsinØ or sinØ = y/r
also x^2 + y^2 = r^2
so letus put all these values in r = 7cos(pheta) - 3sin(pheta)
then in your equation r = 7(x/r) - 3(y/r)
multiply by r both sides
r^2 = 7x - 3y
x^2 + y^2 = 7x - 3y
x^2 - 7x + y^2 + 3y = 0