# Power Series

Hi ive got 2 questions im not to sure about.

1.Evaluate sinh(1.6), correct to 5 decimal places, using power series methods.
I think i got the answer to this as being 3.16200 by using the series expansion for sinh "x" and putting 1.6 into the equation.

2.Determine the power series for, cos 4t, as far as the term which includes, t6.
Ive no idea what this is about is it using the cosh x series expansion rule or something?

Im using the book "higher engineering mathematics" by John Bird if anyone has any page references or tips.

Thanks

HallsofIvy
Homework Helper
tone999 said:
Hi ive got 2 questions im not to sure about.

1.Evaluate sinh(1.6), correct to 5 decimal places, using power series methods.
I think i got the answer to this as being 3.16200 by using the series expansion for sinh "x" and putting 1.6 into the equation.
Since it is easy to check by calculator that
$$sinh(1.6)= (e^{1.6}-e^{-1.6})/2= 2.37557$$
no, that's not at all correct. Since you don't say exactly what the series you used was, I don't where you might have made an error.

2.Determine the power series for, cos 4t, as far as the term which includes, t6.
Ive no idea what this is about is it using the cosh x series expansion rule or something?
Why should it have anything to do with cosh x? Are is this a typo? Are you asked for the power series for cosh(4t)? You are asked for the power series for cos(4t). Do you know how to calculate a Taylor's series? If you already know the Taylor's series for cos(x), just replace x by 4t.

Im using the book "higher engineering mathematics" by John Bird if anyone has any page references or tips.

Thanks