If quadratic equations $a_1x^2 + b_1x + c_1 = 0$ and $a_2x^2 + b_2x + c_2 = 0$ have both their roots common then they satisy, $$\frac{a_1}{a_2} = \frac{b_1}{b_2} = \frac{c_1}{c_2}$$
But even if both the quadratic equations have only one common root say $\alpha$ then at $x=\alpha$
$$a_1\alpha^2 + b_1\alpha + c_1 = 0 \implies \frac{a_1}{c_1}\alpha^2 + \frac{b_1}{c_1}\alpha =-1$$ $$similarly$$ $$a_2\alpha^2 + b_2\alpha + c_2 = 0 \implies \frac{a_2}{c_2}\alpha^2 + \frac{b_2}{c_2}\alpha =-1$$
which on comparing gives me $$\frac{a_1}{c_1} = \frac{a_2}{c_2}, \space \frac{b_1}{c_1} = \frac{b_2}{c_2} \implies \frac{a_1}{a_2} = \frac{b_1}{b_2} = \frac{c_1}{c_2}$$
Where am I going wrong in understanding this?