Let ℝ denote the set of all real numbers. For a real number x, let [x] denote the greatest integer ≤ x. Let n denote a natural number.
Match each entry in List-I to the correct entry in List-II and choose the correct option.
| List-I | List-II |
|---|---|
|
(P) The minimum value of n for which the function f(x) = [ (10x³ − 45x² + 60x + 35) / n ] is continuous on the interval [1, 2], is |
(1) 8 |
|
(Q) The minimum value of n for which g(x) = (2n² − 13n − 15)(x³ + 3x), x ∈ ℝ, is an increasing function on ℝ, is |
(2) 9 |
|
(R) The smallest natural number n which greater than 5, such that x = 3 is a point of local minima of h(x) = (x² − 9)ⁿ (x² + 2x + 3), is |
(3) 5 |
|
(S) Number of x₀ ∈ ℝ such that f(x) = Σ (k = 0 to 4) [ sin|x − k| + cos|x − k + 1/2| ], is NOT differentiable at x₀, is |
(4) 6 |
| (5) 10 |
Correct Answer :
(P)→(2), (Q)→(1), (R)→(4), (S)→(3)
Solution :
We are given the four entries in List-I and need to match them with the correct values in List-II.
Analysis of Entry (P):
Let .
To understand the behavior of on the interval , we find its derivative:
.
For , we have , meaning is a decreasing function on this interval.
The boundary values of are:
.
Thus, the range of on is .
For the greatest integer function to be continuous on , it must be constant. This requires that the interval does not contain any integers in its interior, and if it contains an integer as a boundary, it must not cause a discontinuity.
Let's check the natural number values for :
If , the interval is , which contains the integer , causing a discontinuity.
If , the interval is . This interval does not contain any integers since and .
Thus, the minimum value of is .
Therefore, (P) → (2).
Analysis of Entry (Q):
We are given .
Let . Its derivative is , so is strictly increasing on .
For to be an increasing function, the coefficient must be non-negative:
Factoring the expression:
.
Since is a natural number, . Hence, we must have:
.
The minimum natural number satisfying this inequality is .
Therefore, (Q) → (1).
Analysis of Entry (R):
We are given .
For a neighborhood around , let .
Since , remains strictly positive in a small interval around .
Thus, the sign and extremum properties of near depend entirely on .
For to be a local minimum, we must have in a neighborhood of .
This requires for all near , which is true if and only if is an even integer.
We are looking for the smallest natural number . Since must be even, the smallest such number is .
Therefore, (R) → (4).
Analysis of Entry (S):
We have the function:
.
Let us evaluate each term of the sum:
1. since cosine is an even function. Therefore, is differentiable everywhere on .
2. For , at :
- The right-hand derivative is .
- The left-hand derivative is .
Thus, is not differentiable at .
Since the summation runs from to , the points of non-differentiability are exactly .
The number of such points is .
Therefore, (S) → (3).
Combining all the results, we get the matching:
(P)→(2), (Q)→(1), (R)→(4), (S)→(3).
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