Help? i've tried for almost an hour and cannot figure out how to do this problem!

convert the polar equation to rectangular form r=2sinθ-4cosθ

the answer is supposed to be (x+2)^2 + (y-1)^2 =5

but i dont know how to get there :(

Remember these three things:

r^2 = x^2 + y^2
y = r * sin(t)
x = r * cos(t)

r = 2 * sin(t) - 4 * cos(t)
r * r = r * (2 * sin(t) - 4 * cos(t))
r^2 = 2 * r * sin(t) - 4 * r * cos(t)
x^2 + y^2 = 2 * y - 4 * x
x^2 + 4x + y^2 - 2y = 0
x^2 + 4x + 4 + y^2 - 2y + 1 = 0 + 4 + 1
(x + 2)^2 + (y - 1)^2 = 5

NOTE: Notice my "trick" was to multiply everything by r. After that, it was nothing more than substitution and algebra.