Find the coefficient of x5 in the expansion of (1 + x)3 (1 – x)6.
To Find : coefficient of x5
For (1+x)3
a=1, b=x and n=3
We have a formula,
For (1-x)6
a=1, b=-x and n=6
We have formula,
We have a formula ,
By using this formula, we get,×
Coefficients of x5 are
x0.x5 = 1× (-6)=-6
x1.x4 = 3×15=45
x2.x3 = 3×(-20)=-60
x3.x2 = 1×15=15
Therefore, Coefficients of x5 = -6+45-60+15 = -6
Conclusion : Coefficients of x5 = -6