Thanks for your help. I did use the taylor and then the convert/polynom. however I cannot store into function where i can then input any value for x. For example i did the following:

f :=x->convert(taylor(1/(1-x),x=0,4),polynom)

but the tayping f(3) gives the error:

Error, (in f) invalid input: taylor received 3 = 0, which is not valid for its 2nd argument, eqn

I do see why the error is generated. but knowing the answer to this 4 term expansion is:    1+x+x^2+x^3

how can i input something into it, like f(3)= 1+3+9+27

Sorry for these probably simple questions.

Thank you in advance

Thanks for your help. I did use the taylor and then the convert/polynom. however I cannot store into function where i can then input any value for x. For example i did the following:

f :=x->convert(taylor(1/(1-x),x=0,4),polynom)

but the tayping f(3) gives the error:

Error, (in f) invalid input: taylor received 3 = 0, which is not valid for its 2nd argument, eqn

I do see why the error is generated. but knowing the answer to this 4 term expansion is:    1+x+x^2+x^3

how can i input something into it, like f(3)= 1+3+9+27

Sorry for these probably simple questions.

Thank you in advance