Then, the value of lim f (n) is equal to : 17100 A 3 + 4/3 * ln(7) 4 - 3/4 * ln(7/3) 4 - 4/3 * ln(7/3) 3 + 3/4 * ln(7) f(n)= n + (16 + 5n - 3n ^ 2)/(4n + 3n ^ 2) + (32 + n - 3n ^ 2)/(8n + 3n ^ 2) + (48 - 3n - 3n ^ 2)/(12n + 3n ^ 2) +***+ 25n-7n^ 2 7n^ 2 .
Detailed Explanation
1. Recognising the pattern
Write the function more neatly for a fixed positive integer :
Why does that numerator look so weird? Because the popular trick “add 1 and subtract 1” is hidden inside it!
2. Kill the big– explosion
Each term inside the sum is roughly (because the and dominate). Summing over terms gives , which cancels the lonely leading . So everything infinite disappears and you are left with a finite expression:
Therefore
3. Spotting the Riemann sum
Factor out from numerator and denominator:
Put (right-end points of equal sub-intervals on ). Then
Hence
This is exactly the right-Riemann sum for
4. Compute the integral
Do a quick long division:
So
5. Limit value
Therefore
Among the four options, that matches Option B.
Simple Explanation (ELI5)
What is the question?
You have a long-looking fraction–sum that depends on a number . The question asks, “When becomes a really, really huge number, what does the whole expression settle down to?”
How to think about it (like a story)
- Picture as the number of tiny steps along a road from 0 to 1.
- Each fraction in the sum is like measuring the height of a curve at one of those steps.
- Adding all those little heights and multiplying by the step–width () is the same trick we use to turn a sum into an area under a curve (this is what grown-ups call a Riemann sum).
- When is gigantic, the road has millions of tiny steps, so the sum is almost exactly the integral of that curve from 0 to 1.
- Once you spot the right curve, doing the integral is easy and gives a nice clean number with a small natural‐log piece.
That final number is the answer!
Step-by-Step Solution
Step–by–step calculation
-
Rewrite
-
Separate out the “”
Hence
-
Normalise each term
Divide top and bottom by and set : -
Recognise the Riemann sum
As this becomes the integral -
Integrate
Long-divide:Then
-
Final answer
This is Option (2) (or B) from the list.
Examples
Example 1
Estimating the area under a speed–time graph by adding many thin rectangles (Riemann sum) and then shrinking their width to zero (integral).
Example 2
In probability, converting the sum of binomial probabilities into an integral to approximate a normal distribution (De Moivre–Laplace).
Example 3
Using long division to integrate rational functions in electronics when finding the average power over one period of a signal.
Visual Representation
References
- [1]Thomas' Calculus – Chapters on Riemann Sums and Definite Integrals
- [2]MIT OpenCourseWare – Single-Variable Calculus, Lecture on Riemann Sums
- [3]I. A. Maron's Problems in Calculus of One Variable – Problems on using limits of sums
- [4]G. B. Thomas & Ross L. Finney, Calculus and Analytic Geometry (technique of adding/subtracting 1 in limits)