Find the positive integer n such that the expansion of (4x - 7y)^n contains a term of the form cx^2*y.
+6 Hello
If a and b are real numbers and n is a positive integer, then
(a + b)
n
=nC0
a
n + nC1
a
n – 1 b
1
+ nC2
a
n – 2 b
2
+ ...
... + nCr
a
n – r
br
+ ... + nCn
b
n
, where nCr
=
n
r n r −
for 0 ≤ r ≤ n
The general term or (r + 1)th term in the expansion is given by
Tr + 1 = nCr
a
n–r b
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