(1-x)^n
= 1 + n(-x) + n(n-1)/2! (-x)^2 + n(n-1)(n-2)/3! (-x)^3 + ...
= 1-6x+ax^2+bx^3
so -nx = -6x
n = 6
n(n-1)/2! (-x)^2 = ax^2
6(5)/2=a
a = 15
n(n-1)(n-2)/3! (-x)^3 = bx^3
6(5)(4)/6 = -b
b = -20
the first four terms in the expansion of (1-x)^n are 1-6x+ax^2+bx^3.find the n and also the respective value for a and b
1 answer