The question is rather incomplete. It asks you to work out the first four terms - what does this mean? There is no general convention about what the first four terms are. It should really specify if it is the first four terms in ascending powers of x that it wants or the first four descending powers of x that it wants.
Nonetheless, what have you tried so far?
What is the binomial expansion of (x+y)12? Work out the first four (ascending/descending) terms of that and substitute into your expansion x=x3,y=−21x.
The question is rather incomplete. It asks you to work out the first four terms - what does this mean? There is no general convention about what the first four terms are. It should really specify if it is the first four terms in ascending powers of x that it wants or the first four descending powers of x that it wants.
Nonetheless, what have you tried so far?
What is the binomial expansion of (x+y)12? Work out the first four (ascending/descending) terms of that and substitute into your expansion x=x3,y=−21x.
So I have started by --->This is meant to show 12 choose 0 (12/0)(x^3)^12 + (12/1)(x^3)&11(1/2x)+(12/2)(x^3)^10(1/2x)^2+(12/3)(x^3)^9(1/2x)^3