NIMCET 2011 — Mathematics PYQ
NIMCET | Mathematics | 2011The least integral value of k for which (k - 2)x^2 + 8x + k + 4 > 0 for all x∈R, is:
Choose the correct answer:
- A.
5
(Correct Answer) - B.
4
- C.
3
- D.
6
5
Explanation
1. First Condition (a > 0):
In our equation, a=k−2.
2. Second Condition (D < 0):
The discriminant is D=b2−4ac. Here, a=(k−2), b=8, and c=(k+4).
Divide the entire inequality by 4 to simplify:
Multiply by −1 (and reverse the inequality sign):
3. Solve the Quadratic Inequality:
Factorize the expression:
The critical values are k=−6 and k=4. For the expression to be greater than zero:
4. Combine All Conditions:
We have:
-
k > 2 (from the first condition)
-
k < -6 or k > 4 (from the second condition)
The intersection of these conditions is k > 4.
5. Find the Least Integral Value:
Since k must be an integer and k is strictly greater than 4, the smallest integer value is:
The correct option is (a) 5.
