Try the following GMAT Quantitative Reasoning question on how the coefficients of a quadratic equation impact the nature of the roots.
Question 71:
The values of $m$ for which the quadratic equation $4x^2 + x – mx + 1=0$ has real and equal roots are

$\quad 3 \; \textrm{and} \; 5$

$\quad 3 \; \textrm{and} \; 5$

$\quad 3 \; \textrm{and} \; 5$

$\quad 3 \; \textrm{and} \; 5$

$\quad 3 \; \textrm{only}$