CA Foundation · Quantitative Aptitude · Equations
For what value of k does the equation kx² − 12x + 9 = 0 have two equal real roots?
The equation has equal roots only when the discriminant is zero. Here b²−4ac equals 144−36k, which is zero when k equals 4. So k is 4. Other values such as 16 come from wrongly dividing 144 by 9 instead of 36.
- A3
- B4Correct
- C8
- D16
Explanation
Equal roots need the discriminant b² − 4ac to be zero. Here 144 − 4(k)(9) = 144 − 36k = 0, so k = 4. The value 16 results from wrongly dividing 144 by 9 rather than by 36.
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