In the binomial expansion (x+k/x)^7, where k is a positive constant, the coefficients of x^3 and x are the same. Find the value of k.
Using the value of k found in part (i), find the coefficient of x^7 in the expansion (1-5x^2)(x+k/x)^7.
Need major help on the first part? Thanks in advance. :)

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\[(x + \frac{k}{x})^7\]
\[(1 - 5x^2)(x + \frac{k}{x})^7\]

for first one, did you solve
\[35k^3=21k^2\]?

No, I'm completely at a lost here. Sorry. :(

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