A quadratic equation in the form of 3x² - 5x + 2 = 0.

Mentally compute $b^2$ ($25$) and subtract $4 imes a imes c$ ($4 imes 3 imes 2 = 24$) in under 5 seconds.

Students often miss the negative sign of coefficient $b$ or confuse the coefficients $a, b, c$ when the equation is not written in standard form.

If the discriminant $D > 0$, the quadratic equation has two distinct real roots; if $D=0$, roots are real and equal; if $D<0$, roots are imaginary.