sum from n=1 to infinity of n(7/8)^n

解答

n = 1 \sum \infty n (\frac{7}{8})^{n}

收敛

求解步骤

n = 1 \sum \infty n (\frac{7}{8})^{n}

使用级数比值审敛法:

收敛

= 收敛

d er i v a t i v e x^{2} + 4 x + 5

\frac{\partial}{\partial x} (x (y - 1))

\frac{d}{d x} (x^{2} lo g_{2} (x))

t an g e n t (x^{3} - 25 x)^{12} (- 5)

\frac{d}{d t} (\frac{( 2 t + 1 ) ^{\frac{3}{2}}}{3})