Find $a$, $b$ and $c$ so the line $y=x$ can be a tangent of the parabola $y=ax^2+ bx+c$ at the point $x=1$. The parabola passes from the point $M(-1;0)$. So I formed the system $2a+b=1$ $a-b+c=0$ How do I solve this system?
Details : From $y=x$ we see that $k=1$ (we also have that $x=1$) so $2\cdot a\cdot 1+b\cdot 1=1$