- #1
songoku
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Homework Statement
Find
$$\sum_{k=1}^{64} {64 \choose k} 64k$$
Homework Equations
Not sure
The Attempt at a Solution
Please give me hint how to start doing this question
songoku said:Homework Statement
Find
$$\sum_{k=1}^{64} {64 \choose k} 64k$$
Homework Equations
Not sure
The Attempt at a Solution
Please give me hint how to start doing this question
songoku said:Homework Statement
Find
$$\sum_{k=1}^{64} {64 \choose k} 64k$$
Homework Equations
Not sure
The Attempt at a Solution
Please give me hint how to start doing this question
PeroK said:Work it out for n = 1, 2, 3, 4, 5 and see whether you can spot a pattern. Then, perhaps, try induction on ##n## to prove a general formula. Finally, set ##n = 64##
Ray Vickson said:Here is a little hint for a non-calculus solution, using n = 4 instead of n = 64. Note that for ##k =0## we have ##0 {4 \choose 0} = 0##, so we can start the summation from ##k = 0## instead of ##k = 1##. Let ##S_4 = \sum_{k=0}^4 k {4 \choose k}##. We have
$$S_4 = 0 {4 \choose 0} + 1 {4 \choose 1} + 2 {4 \choose 2} + 3 {4 \choose 3} + 4 {4 \choose 4}$$.
However, we have ##{n \choose k} = {n \choose n-k}## for all ##k##, so we can write
$$S_4 = 0 {4 \choose 4} + 1 {4 \choose 3} + 2 {4 \choose 2} + 3 {4 \choose 1} + 4 {4 \choose 0} $$.
Now add the two forms together, collecting coefficients of each ##{4 \choose j}##. That will give you
$$2S_4 = (0+4) {4 \choose 0} + (1+3) {4 \choose 1} + \cdots + (4 + 0) {4 \choose 4} = 4 \sum_{k=0}^4 {4 \choose k}.$$
Do you recognize that last summation?
haruspex said:A standard method for getting rid of an awkward factor consisting of the index variable (the k in 64k) is to make the sum a function of some unknown, s say, by multiplying the kth term by s to some power. E.g.
$$\sum_{k=1}^{64} {64 \choose k} 64k s^k$$
What would happen if you tried to integrate that wrt s? Ok, so try a slightly different power.
Yes, that's the right step.songoku said:I try to use sk-1 and after integration with respect to s, I get 64Ck . 64 . sk
haruspex said:Yes, that's the right step.
Do you not recognise that sum? (Binomial Theorem.)
Keep it as an indefinite integral. You will need to differentiate wrt s later.songoku said:integrating both sides, I get:
haruspex said:Keep it as an indefinite integral. You will need to differentiate wrt s later.
Not yet. Sum it first.songoku said:Then I differentiate it with respect to s?
So:haruspex said:Not yet. Sum it first.
The sequence is: multiply by sk-1, integrate, perform the sum, differentiate wrt s, plug in s=1.
No, you have not performed the sum. You have left it as a Σ. It sums easily into a closed form.songoku said:Am I doing it correctly?
haruspex said:No, you have not performed the sum. You have left it as a Σ. It sums easily into a closed form.
You are familiar with the binomial theorem, yes?
You got it.songoku said:I have learned about binomial theorem but I am trying to figure out how to use it for this question.
Let me try again:
$$\int U_{k} ~ ds = {64 \choose k} 64 s^{k} $$
$$\sum_{k=0}^{k=64} \int U_{k} ~ ds =\sum_{k=0}^{k=64} {64 \choose k} 64 s^{k} $$
$$=64 (1+s)^{64}$$
Differentiate both sides with respect to s:
$$\sum_{k=0}^{k=64} U_{k} = 64^{2} (1+s)^{63}$$
Put s = 1:
$$\sum_{k=0}^{k=64} U_{k} = 64^{2} (2)^{63}$$
$$=2^{75}$$
Is this how I suppose to do it?
The formula for the value of summation involving combination is:
∑k=0n (n choose k) * ak * bn-k
where n is the number of terms, a and b are constants, and (n choose k) represents the combination of n and k.
To solve a summation involving combination, you can follow these steps:
1. Identify the values of n, a, and b in the formula.
2. Calculate the combination of n and k for each term.
3. Substitute the values into the formula and simplify.
4. If possible, use algebraic manipulation to further simplify the expression.
5. Evaluate the expression to get the final answer.
The value of summation involving combination is important because it allows us to calculate the total number of possible combinations of a given set of items. This can be useful in various fields, such as statistics, probability, and computer science.
No, the value of summation involving combination cannot be negative. Combination values can only be positive integers, and when multiplied by constants and added together, the resulting summation value will also be positive.
Yes, there are many real-life applications of summation involving combination, such as:
- Calculating the number of possible outcomes in a game of chance
- Determining the total number of combinations in a lock or passcode
- Analyzing the probability of certain events occurring in a given situation
- Creating efficient algorithms for data compression and error correction
- Studying the genetics of inherited traits and possible combinations of genes.