Question Details

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

Options

A

(P)→(1), (Q)→(3), (R)→(2), (S)→(5)

B

(P)→(2), (Q)→(1), (R)→(4), (S)→(3)

C

(P)→(5), (Q)→(1), (R)→(4), (S)→(3)

D

(P)→(2), (Q)→(3), (R)→(1), (S)→(5)

Show Answer

Correct Answer :

Option B

(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 gx=10x3-45x2+60x+35.
To understand the behavior of gx on the interval 12, we find its derivative:
gx=30x2-90x+60=30x-1x-2.
For x12, we have gx0, meaning gx is a decreasing function on this interval.
The boundary values of gx are:
g1=10-45+60+35=60
g2=108-454+602+35=80-180+120+35=55.
Thus, the range of gxn on 12 is 55n60n.

For the greatest integer function fx=gxn to be continuous on 12, it must be constant. This requires that the interval 55n60n 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 n:
If n=8, the interval is 6.8757.5, which contains the integer 7, causing a discontinuity.
If n=9, the interval is 6.116.67. This interval does not contain any integers since 6<6.11 and 6.67<7.
Thus, the minimum value of n is 9.
Therefore, (P) → (2).

Analysis of Entry (Q):
We are given gx=2n2-13n-15x3+3x.
Let kx=x3+3x. Its derivative is kx=3x2+3>0, so x3+3x is strictly increasing on .
For gx to be an increasing function, the coefficient must be non-negative:
2n2-13n-150
Factoring the expression:
2n-15n+10.
Since n is a natural number, n+1>0. Hence, we must have:
2n-150n7.5.
The minimum natural number satisfying this inequality is n=8.
Therefore, (Q) → (1).

Analysis of Entry (R):
We are given hx=x2-9nx2+2x+3=x-3nx+3nx2+2x+3.
For a neighborhood around x=3, let Px=x+3nx2+2x+3.
Since P3=6n18>0, Px remains strictly positive in a small interval around x=3.
Thus, the sign and extremum properties of hx near x=3 depend entirely on x-3n.
For x=3 to be a local minimum, we must have hxh3=0 in a neighborhood of x=3.
This requires x-3n0 for all x near 3, which is true if and only if n is an even integer.
We are looking for the smallest natural number n>5. Since n must be even, the smallest such number is n=6.
Therefore, (R) → (4).

Analysis of Entry (S):
We have the function:
fx=k=04sinx-k+cosx-k+12.
Let us evaluate each term of the sum:
1. cosθ=cosθ since cosine is an even function. Therefore, cosx-k+12=cosx-k+12 is differentiable everywhere on .
2. For sinx-k, at x=k:
- The right-hand derivative is limh0+sinh-0h=1.
- The left-hand derivative is limh0+sinh-0-h=-1.
Thus, sinx-k is not differentiable at x=k.
Since the summation runs from k=0 to 4, the points of non-differentiability are exactly x01234.
The number of such points x0 is 5.
Therefore, (S) → (3).

Combining all the results, we get the matching:
(P)→(2), (Q)→(1), (R)→(4), (S)→(3).

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