Hello, I try to get the algebraic proof of this theorem. I follow this https://i2.paste.pics/796e202e27015761ebe45897e885b151.png. I understand how the author derived the final solution for the case of two solutions, namely PQ and PR but I don't understand the case of a single solution. How can that be [MATH]PT^2[/MATH] when the solution of a quadratic equation for a single root is just [MATH]\frac{-b}{2a}[/MATH] which for this case is just [MATH]-1[/MATH].
Also, since we assume [MATH]C(x,y) = 0 [/MATH] does it mean the product of root (two root) or a square of a single root is equal to 0?
Thanks
Also, since we assume [MATH]C(x,y) = 0 [/MATH] does it mean the product of root (two root) or a square of a single root is equal to 0?
Thanks