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Prove the following formulae are true: \[\begin{aligned} a^{n + 1} - b^{n + 1} &= (a - b) (a^n + a^{n-1}b + \dots + b^n);\\ a^{2n + 1} + b^{2n + 1} &= (a + b) (a^{2n} - a^{2n-1}b + a^{2n-2}b^2 - \dots + b^{2n}). \end{aligned}\]

For a given polynomial \(P (x)\) we describe a method that allows us to construct a polynomial \(R (x)\) that has the same roots as \(P (x)\), but all multiplicities of 1. Set \(Q (x) = (P(x), P'(x))\) and \(R (x) = P (x) Q^{-1} (x)\). Prove that

a) all the roots of the polynomial \(P (x)\) are the roots of \(R (x)\);

b) the polynomial \(R (x)\) has no multiple roots.

Prove that for \(n> 0\) the polynomial \(nx^{n + 1} - (n + 1) x^n + 1\) is divisible by \((x - 1)^2\).

Let it be known that all the roots of some equation \(x^3 + px^2 + qx + r = 0\) are positive. What additional condition must be satisfied by its coefficients \(p, q\) and \(r\) in order for it to be possible to form a triangle from segments whose lengths are equal to these roots?