66.4: Useful Series
( \newcommand{\kernel}{\mathrm{null}\,}\)
The first four series are valid if |x|<1; the fifth is valid for x2<a2; and the last three are valid for all real x.
(1+x)1/2=1+12x−18x2+116x3−5128x4+7256x5−211024x6+332048x7−42932768x8+⋯ (D.1) (1−x)1/2=1−12x−18x2−116x3−5128x4−7256x5−211024x6−332048x7−42932768x8−⋯ (D.2) (1+x)−1/2=1−12x+38x2−516x3+35128x4−63256x5+2311024x6−4292048x7+643532768x8−⋯ (D.3) (1−x)−1/2=1+12x+38x2+516x3+35128x4+63256x5+2311024x6+4292048x7+643532768x8+⋯ (D.4) 1a+x=1a−xa2+x2a3−x3a4+x4a5−x5a6+⋯ex=1+x+x22+x36+x424+x5120+x6720+x75040+x840320+x9362880+⋯sinx=x−x36+x5120−x75040+x9362880−x1139916800+x136227020800−⋯cosx=1−x22+x424−x6720+x840320−x103628800+x12479001600−⋯