Eamon R.
asked 07/29/21Which is the correct taylor series
Find the Taylor series for f(x)=2xe−3x at x=4 and its interval of convergence.
∑n=0∞1/n! e-12(8(−3)n−2n(−3)n-1)(x−4)n,(−∞,∞)
∑n=0∞1/n! e-12(8(−3)n+2n(−3)n-1)(x−4)n,(−∞,∞)
∑n=0∞1/n! e-122n(−3)n-1(x−4)n,(−∞,∞)
∑n=0∞1/n! e-128n(−3)n(x−4)n,(−∞,∞)
1 Expert Answer
Bradford T. answered 07/30/21
Retired Engineer / Upper level math instructor
f(x)=2xe-3x --> f(4) =8e-12
f'(x)=2e-3x-6xe-3x --> f'(4) = -22e-12
f''(x) = -6e-3x-6e-3x+18xe-1x --> f"(4) =-6e-12-6e-12+72e-12 = 60e-12
...
Looking at only the coefficients for e-12 -->8, -22, 60,...
8(-3)n+2n(-3)n-1 fits for n = 0,1,2
So the second choice is the answer.
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Andrew D.
07/30/21