A student solved the given quadratic equation in the following way :

Which of the following represents the error committed by the student ?

Correct option is C

Explanation
The student correctly completed the square and obtained the equation:
(x + 3)² = 36
Taking the square root of both sides gives:
x + 3 = ±6
Now solve both cases:
Positive root
x + 3 = 6
x = 3
Negative root
x + 3 = −6
x = −9
The mistake occurred because the student considered only the positive value of 6 and ignored the negative value. A quadratic equation normally has two solutions, so both must be included.
Additional Information (Other Options)
If the right-hand side were 0, the equation would have only one solution.
If the right-hand side were negative, there would be no real solutions.
Since 36 is positive, two real solutions exist.