Part of ALG-03 — Sequences & Series (AP, GP, Special Series)

Insertion of Means

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Inserting k Arithmetic Means between a and b: The k means form an AP with a and b: a, A1A_1, A2A_2, ..., AkA_k, b Total terms = k+2, so d = ba(k+1)\frac{b-a}{(k+1)} AiA_i = a + i*d = a + iba(k+1)\frac{b-a}{(k+1)} Sum of k AMs = ka+b2\frac{a+b}{2}

Inserting k Geometric Means between a and b: The k means form a GP with a and b: a, G1G_1, G2G_2, ..., GkG_k, b Total terms = k+2, so r = ba\frac{b}{a}^{1k+1\frac{1}{k+1}} GiG_i = a * rir^i Product of k GMs = (ab)^{k/2}

Key result: The sum of n AMs between a and b = n times the single AM = na+b2\frac{a+b}{2}. Similarly, the product of n GMs = (GM)^n = (ab)^{n/2}.

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