# Finding the polar equation

1. Jan 26, 2014

### ThiagoG

1. The problem statement, all variables and given/known data
Find a polar equation for the curve represented by the Cartesian equation.

y=1+3x

2. Relevant equations
x2+y2=r2
x=Rcos(θ)
y=Rsin(θ)

3. The attempt at a solution
(1+3x)2+x2=r2
1+6x+10x2=r2
1+6rcos(θ)+10r2cos2(Θ)=r2

2. Jan 26, 2014

### HallsofIvy

Why are you squaring? This will give you a relation between $x^2$ and $y^2$, not x and y, and so not the original equation. Just replace "x" with $r cos(\theta)$ and "y" with $r sin(\theta)$ in the original equations.

3. Jan 26, 2014

### ThiagoG

Oh thank makes a lot of sense. Thank you.