Question

One of the five quadratics below has a repeated root. (The other four have distinct roots.) What is the repeated root?
\begin{align*}
&-x^2 - 18x + 9 \\
&3x^2 - 6x + 12 \\
&8x^2 - 32x - 128 \\
&25x^2 - 30x + 64 \\
&x^2 - 14x + 49
\end{align*}

Answer 1

x^2 - 14x + 49 = (x-7)^2 has discriminant 14^2 - 4·49 = 0, so the repeated root is 7.