What is the coefficient of in the power series expansion of ? I'm having trouble expanding this. Could someone explain how to solve it? Cheers.
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Originally Posted by Haris What is the coefficient of in the power series expansion of ? I'm having trouble expanding this. Could someone explain how to solve it? Cheers. you don't need to expand anything let $\displaystyle f(x) = \frac 1{(9 + 5x)^{1/4}}$ the coefficient of the $\displaystyle x^2$-term is given by $\displaystyle \frac {f''(0)}{2!}$
Originally Posted by Haris What is the coefficient of in the power series expansion of ? I'm having trouble expanding this. Could someone explain how to solve it? Write it as $\displaystyle 9^{-1/4}\bigl(1+\tfrac{5x}9\bigr)^{-1/4}$. Then use the binomial expansion of $\displaystyle (1+t)^{-1/4}$, taking t=5x/9. Edit. Alternatively, use Jhevon's method. It's equally good.
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