Skip to main contentSkip to solution

The number of non-negative integer values of kk for which the quadratic equation x2−5x+k=0x^2 - 5x + k = 0 has only integer roots, is

Entered answer:

Solution

✅ Correct Answer: 3

Given the quadratic equation x2−5x+k=0x^2 - 5x + k = 0, where kk is a non-negative integer and both roots are integers.


Let the two integer roots be α\alpha and β\beta.

Comparing with x2−5x+k=0x^2 - 5x + k = 0:

α+β=5\alpha + \beta = 5 (sum of roots)

α⋅β=k\alpha \cdot \beta = k (product of roots)


Since k≥0k \geq 0, the product of roots is non-negative, meaning both roots must be non-negative integers.

Listing all pairs of non-negative integers that add up to 5:

α=0, β=5⇒k=0×5=0\alpha = 0,\ \beta = 5 \Rightarrow k = 0 \times 5 = 0

α=1, β=4⇒k=1×4=4\alpha = 1,\ \beta = 4 \Rightarrow k = 1 \times 4 = 4

α=2, β=3⇒k=2×3=6\alpha = 2,\ \beta = 3 \Rightarrow k = 2 \times 3 = 6

The remaining pairs (3,2), (4,1), (5,0)(3,2),\ (4,1),\ (5,0) give the same values of kk.


The distinct non-negative integer values of kk are: 0, 4, 60,\ 4,\ 6

Therefore, the number of non-negative integer values of kk =3= \boxed{3}

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question