Skip to content

CA Foundation · Quantitative Aptitude · Equations

What is the sum of all the roots of the cubic equation 2x³ − 6x² + 5x − 7 = 0?

The sum of the roots is 3. For a cubic ax³ + bx² + cx + d = 0, the roots add up to −b/a, which here is −(−6)/2 = 3. Choosing −3 results from ignoring the negative sign in the formula.

  1. A−3
  2. B3Correct
  3. C5/2
  4. D7/2

Explanation

For a cubic ax³ + bx² + cx + d = 0, the sum of the roots is −b/a. Here a = 2 and b = −6, so the sum = −(−6)/2 = 3. The value −3 comes from forgetting the sign change, and 5/2 is c/a, which is not the sum of the roots.

Did you get it right without looking?

One question tells you little. A timed set on Equations shows your real accuracy, how long you take and where you lose marks.

Practise EquationsFree diagnostic mock

More Equations questions