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MATU • Trigonometria
MATU_TRI_534
Propio
Enunciado
Demuestre que:
$$ \arctan\left(\frac{1}{3}\right) + \arctan\left(\frac{2}{9}\right) + \arctan\left(\frac{4}{33}\right) + \dots \text{ al } \infty = \frac{\pi}{4} $$
$$ \arctan\left(\frac{1}{3}\right) + \arctan\left(\frac{2}{9}\right) + \arctan\left(\frac{4}{33}\right) + \dots \text{ al } \infty = \frac{\pi}{4} $$
Solución Paso a Paso
1. Identificación del patrón:
Analizamos los términos:
$T_1 = \arctan\left(\frac{1}{1+2}\right) = \arctan\left(\frac{2-1}{1+2\cdot 1}\right) = \arctan(2) - \arctan(1)$
$T_2 = \arctan\left(\frac{2}{1+8}\right) = \arctan\left(\frac{4-2}{1+4\cdot 2}\right) = \arctan(4) - \arctan(2)$
$T_3 = \arctan\left(\frac{4}{1+32}\right) = \arctan\left(\frac{8-4}{1+8\cdot 4}\right) = \arctan(8) - \arctan(4)$
2. Generalización:
El término $n$-ésimo es:
$$ a_n = \arctan(2^n) - \arctan(2^{n-1}) $$
3. Suma de la serie:
La suma parcial $S_n$ es:
$$ S_n = \sum_{k=1}^{n} [\arctan(2^k) - \arctan(2^{k-1})] $$
$$ S_n = \arctan(2^n) - \arctan(2^0) = \arctan(2^n) - \arctan(1) $$
4. Límite al infinito:
$$ S_\infty = \lim_{n \to \infty} [\arctan(2^n) - \frac{\pi}{4}] $$
Como $\lim_{x \to \infty} \arctan(x) = \frac{\pi}{2}$:
$$ S_\infty = \frac{\pi}{2} - \frac{\pi}{4} = \frac{\pi}{4} $$
$$ \boxed{\frac{\pi}{4}} $$
Analizamos los términos:
$T_1 = \arctan\left(\frac{1}{1+2}\right) = \arctan\left(\frac{2-1}{1+2\cdot 1}\right) = \arctan(2) - \arctan(1)$
$T_2 = \arctan\left(\frac{2}{1+8}\right) = \arctan\left(\frac{4-2}{1+4\cdot 2}\right) = \arctan(4) - \arctan(2)$
$T_3 = \arctan\left(\frac{4}{1+32}\right) = \arctan\left(\frac{8-4}{1+8\cdot 4}\right) = \arctan(8) - \arctan(4)$
2. Generalización:
El término $n$-ésimo es:
$$ a_n = \arctan(2^n) - \arctan(2^{n-1}) $$
3. Suma de la serie:
La suma parcial $S_n$ es:
$$ S_n = \sum_{k=1}^{n} [\arctan(2^k) - \arctan(2^{k-1})] $$
$$ S_n = \arctan(2^n) - \arctan(2^0) = \arctan(2^n) - \arctan(1) $$
4. Límite al infinito:
$$ S_\infty = \lim_{n \to \infty} [\arctan(2^n) - \frac{\pi}{4}] $$
Como $\lim_{x \to \infty} \arctan(x) = \frac{\pi}{2}$:
$$ S_\infty = \frac{\pi}{2} - \frac{\pi}{4} = \frac{\pi}{4} $$
$$ \boxed{\frac{\pi}{4}} $$