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Roodles01
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I have to determine the coefficient of an x term in an expansion such as this;
Determine the coefficient of x^18 in the expansion of (1/14 x^2 -7)^16
The general term in the binomial expansion is
nCk a^k b^(n−k)
I could let
a = (1/14 x^2)
b = -7
n = 16
k = 9?
I have no real idea of how to go about finding this coefficient using the binomial theorem.
Having expanded the expression to the 10th term I get
8C9 (-7) (1/14 x^2)^9
I'm using nCk = n! / (n-k)!k! but can't evaluate this as it is a negative.
I'm assuming that the 8C9 bit is just the opposite of 6th term i.e. 12C5 = 792 (looking at Pascal's triangle this is on the opposite side), but I can get the x^18 bit (I'm assuming the (x^2)^9 can be x^18 here)
Can someone check, please?
Determine the coefficient of x^18 in the expansion of (1/14 x^2 -7)^16
The general term in the binomial expansion is
nCk a^k b^(n−k)
I could let
a = (1/14 x^2)
b = -7
n = 16
k = 9?
I have no real idea of how to go about finding this coefficient using the binomial theorem.
Having expanded the expression to the 10th term I get
8C9 (-7) (1/14 x^2)^9
I'm using nCk = n! / (n-k)!k! but can't evaluate this as it is a negative.
I'm assuming that the 8C9 bit is just the opposite of 6th term i.e. 12C5 = 792 (looking at Pascal's triangle this is on the opposite side), but I can get the x^18 bit (I'm assuming the (x^2)^9 can be x^18 here)
Can someone check, please?
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