December 22, 2014

Homework Help: maths

Posted by Count Iblis on Monday, July 23, 2007 at 2:42am.

Let's denote the three numbers by a1, a2, and a3. Consider the third degree polynomial:

p(x) = (1 + a1 x)(1 + a2 x)(1 + a3 x)

Take the logarithm:

Log[p(x)] =

Log(1 + a1 x) + Log(1 + a2 x)
+ Log(1 + a3 x)

Expand in powers of x by using that:

Log(1 + x) = x - x^2/2 +x^3/3 - x^4/4 + ...

Then, if we denote the sum of the n-th powers of the ai by Sn, we find:

Log[p(x)] = S1 - S2/2 x^2 + S3/3x^3 - S4/4 x^4 + ...

If we now exponentiate this we should get p(x) back:

Exp{Log[p(x)]} = p(x)

We can calculate
Exp[S1 - S2/2 x^2 + S3/3x^3 - S4/4 x^4 + ...]

using the series expansion:

Exp[X] = 1 + X + X^2/2! + X^3/3! + X^4/4! + ...

If we put in here X = S1 - S2/2 x^2 + S3/3x^3 - S4/4 x^4 + ...]

the result must be p(x). Snce p(x) is a third degree polynomial, this means that
all powers of x^4 and higher must vanish.

If you work out the coefficient of x^4 and equate it to zero you get the equation:

S4 = S1^4/6 - S1^2 S2 + S2^2/2 + 4/3 S1 S3

So, if S1 = 4, S2 = 10, and S3 = 22, then S4 must be 50.

the sum of three numbers is 4, the sum of their squares is 10 and the sum of their cubes is 22. what is the sum of their fourth powers?

Answer this Question

First Name:
School Subject:

Related Questions

Algebra - Please solve as polynomial to third degree: the product of three ...
Algebra - Do I have this right? A first degree polynomial crosses the x axis A ...
maths - 1. If the first and third of three consecutive odd integers are added, ...
Maths - true/false 1. a cubic polynomial has at least one zero.............. 2. ...
maths probability - Consider an experiment with four possible outcomes which we ...
calculus--please help!! - I have two questions that I don't understand and need ...
MATHS - The sum of three numbers is 1313. The sum of two of the numbers is 450. ...
maths - Given a positive integer n, let S(n) denote the digit sum of n. Consider...
algebra - Please I do not know how to figure this out: Identify the degree of ...
algebra - Please I do not know how to figure this out: Identify the degree of ...