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| 1. |
Expand in ascending powers of x. cos x, |
| Answer» SOLUTION :`cosx=1/2(E^(is)+e^(-is))=1/2[(1+ix+(i^2x^2)/(2!)+(i^3x^3)/(3!)+...)+(1-ix+(e^2x^2)/(2!)-(i^3x^3)/(3!)+...)]=1/2[2(1-x^2/(2!)+x^4/(4!)-...)]=1-x^2/(2!)+x^4/(4!)-...` | |