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Homework Statement
Find the power series for f(x) using the definition of taylor series expansion about a=9. f(x)=1/sqrt(x)
Homework Equations
The Attempt at a Solution
Find the power series for f(x) using the definition of taylor series expansion about a=9. f(x)=1/sqrt(x)
f(x) = 1/sqrt(x) => f(9) = 1/3
f'(x) = - 1/(2 x^(3/2)) => f'(9) = -1/54
f''(x) = (1*3)/(2^2 x^(5/2)) => f''(9) = 1/324
f'''(x) = -(1*3*5)/(2^3 x^(7/2)) => f'''(9) = 5/5852
...
The patter that seems to be developing is
f^(k)(x) = ( (-1)^k ?)/(2^k x^(1/2 + k) )
but I'm lost as to how to express the pattern that appears in the numerator, hence the question mark, of each order of the function
for f(x) we have 1
for f'(x) we have 1
for f''(x) we have 1*3
for f'''(x) we have 1*3*5
...
The patter that seems to appear after the 1st derivative in a sort of backwards batter, 5*3*1 instead of 1*3*5, is (2k-1)(2k-3)(2k-5)... until the last term is equal to 1
I'm sort of lost... thanks for any help!