They have written 9+4x as 9(1+4x/9) so the square root is 3root(1+4x/9) and then the 3 has cancelled out.
f(x)= 3/sqrt(9+4x) and g(x)= 3/sqrt(1+4x)
i am asked to show that by writing
3/sqrt(9+4x)= 1/sqrt(1+(4x/9)) (and here their is some factor that i know is there, obs) but i cannot see.)
and am then asked to substitute into one of the standard taylor series about 0 for f.give the explicity upto the term x^3 and determine the range of validity.My algebra is letting me down again.I know what i want but i dont know how to get it.
Can anyone help????
Many thanks in advance....