Consider the equation x2 + 4x - n = 0, where n [20, 100] is a natural number. Then the number of all distinct values of n, for which the given equation has integral roots, is equal to
- 6
- 5
- 8
- 7
Answer
(1) 6
Solution
Roots: x = -4 16 + 4n2 = -2 4 + n
Roots are integers ⇔ 4 + n is a perfect square.
∵ 20 n 100 ⇒ 24 4 + n 104
⇒ 4 + n = 25, 36, 49, 64, 81, 100
⇒ n = 21, 32, 45, 60, 77, 96
∴ Number of values of n = 6
Answer: (1)