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


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