JEE MainMathematicsQuadratic Equation and InequalitiesMCQ+4 / −1
The number of integral values of m for which the equation (1 + m2 )x2 – 2(1 + 3m)x + (1 + 8m) = 0 has no real root is :
- A2
- Binfinitely many
- C1
- D3
View written solutionFree
Correct answer: B
- Consider the quadratic equation
For a quadratic equation to have no real root, we need:
- , and
- discriminant .
Here,
Since
for every integral , the equation is always quadratic.
- Compute the discriminant:
So,
That is,
Factor out :
- Expand the terms inside the bracket:
Also,
Therefore,
Simplify:
Factor further:
and since
we get
- For no real roots, require
Thus,
Now, for all integers , and it is zero only when , which is not an integer. Hence for integral ,
So the sign of depends only on .
Therefore,
- Count integral values of :
All positive integers satisfy the condition:
Hence there are infinitely many integral values of .
- Check options:
- A: ❌
- B: infinitely many ✅
- C: ❌
- D: ❌
Therefore, the correct option is B.
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