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You are here: Home » GMAT Problem Solving » Quadratic Equation » Question 3

The GMAT Sample Math question is from the topic Quadratic Equation.

For what value of 'm' will the quadratic equation x² - mx + 4 = 0 have real and equal roots?

1. 16
2. 8
3. 2
4. -4
5. Choice (B) and (C)
   
   

The correct choice is (D) and the correct answer is -4.

Any quadratic equation of the form ax² + bx + c = 0 will have real and equal roots if its discriminant b² - 4ac = 0.

In the given equation x² - mx + 4 = 0, a = 1, b = -m and c = 4.
Therefore, b² - 4ac = m² - 4(4)(1) = m² - 16.

As we know, the roots of the given equation are real and equal.
Therefore, m² - 16 = 0 or m² = 16 or m = +4 or m = -4.

Hence, answer choice (D) is correct.