
Mark M. answered 12/09/23
I love tutoring Math.
When converting between polar coördinates (r, θ) and rectangular coördinates (x, y), the Pythagorean theorem gives us the conversion
r = √(x2 + y2)
Squaring both sides of the above gives us
r2 = x2 + y2
The definitions of sine and cosine give us
y = sin θ
x = cos θ
We will use these because the tan θ in the problem is merely opposite/adjacent = (sin θ)/(cos θ).
Therefore the polar equation
r2 = 10 tan θ
(which is really just r2 = 10 (sin θ)/(cos θ))
becomes the rectangular equation
x2 + y2 = 10y/x