Hint for Section 6.7 Question 3

3. The Binomial Theorem states that given any real numbers a and b and any nonnegative integer n,

(a + b)n = n

(

 n ) an-k   bk
S
k
k=0

The coefficient of  x6 y3  in the expansion of (5x - 3y)9 will occur when k = 3. 

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