Question

Find the value of k for which roots of quadratic equation x² - 4x + k =0 are real and equal.
1. 4
2. - 4
3. 2
4. - 2

Answer 1

Correct Answer - Option 1 : 4

Concept:

Discriminant of quadratic equation ax2 + bx + c = 0, is given by D = b2 - 4ac.

If a quadratic equation ax2 + bx + c = 0 has equal real roots then D = 0.

Calculation:

Given equation x2 - 4x + k =0

If roots of quadratic equation are real and equal then discriminant is zero i.e D = 0 where D = b2 - 4ac.

Here, a = 1, b = - 4 and c = k

⇒ (-4)² - 4⋅ 1⋅ k = 0   

⇒  16 - 4k = 0

⇒ k = 4

Hence, option 1 is correct.