Manipal MET2017MathematicsBinomial Theorem
The coefficient of x in the expansion of (1+x+x^2+x^3 )⁻³ is
Options
- A6
- B9
- C5
- D-3
Correct answer
D. -3
Step-by-step solution
aligned & (1+x+x^2+x^3 )⁻³= [ (x^4-1 ) x-1 ]⁻³ = & (x^4-1 )⁻³(x-1)^3 = & (-1)⁻³ (1-x^4 )⁻³(x-1)^3 = & (-1) (1+3 x^4+ ) (x^3-3 x^2+3 x-1 ) aligned Coefficient of x in (1+x+x^2+x^3 )⁻³ is -3 .