The straight line <span class="math-inline">y = m(x - a)</span> will meet the parabola <span class="math-inline">y^{2} = 4ax</span> in two distinct real points if
<span class="math-inline">m \in R</span>
<span class="math-inline">m \in [-1, 1]</span>
<span class="math-inline">m \in (-\infty, 1] \cup [1, \infty)</span>
<span class="math-inline">m \in R \setminus \{0\}</span>