A1. For which values of $m$ does the graph of the function $f(x)=x^{2}+m x+4$ touch the x-axis?
(A) $m=0$
(B) $m= \pm 4$
(C) $m= \pm 2$
(D) $m=1$ and $m=5$
(E) $m=-1$ and $m=-5$
A1. For the graph of a quadratic function to touch the x-axis, it must hold that $D=0$. We substitute the data into the formula for $D$ and get $D=m^{2}-16$. Setting it equal to 0, we get the solution $m= \pm 4$.