# Binomial Expansion helpWatch

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#1
Write down the expansion of:

(1 - 1/2x)^4

Cud sumbody plz du this line by line as i have absolutely no idea wah 2 du
Your help iz very much appreciated
0
13 years ago
#2
(Original post by Tut)
Write down the expansion of:

(1 - 1/2x)^4

Cud sumbody plz du this line by line as i have absolutely no idea wah 2 du
Your help iz very much appreciated
Use: (a + b)^n = a^n + nC1.a^(n-1).b + nC2.a^(n-2).b^2 + ...nCr.a^(n-r).b^r + ... + b^n

With: a = 1, b = -x/2.

Hence: (1 - x/2)^4 = 1 + 4C1.1^3.(-x/2)^1 + 4C2.1^2.(-x/2)^2 + 4C3.1^1.(-x/2)^3 + 4C4.1^0.(-x/2)^4 = 1 + 4(-x/2) + 6(x^2/4) + 4(-x^3/8) + x^4/16 = 1 - 2x + (3x^2)/2 - (x^3)/2 + (x^4)/16
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