Question 1198624
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There are n+1 = 9+1 = 10 terms total.
The first term has x^9y^0.
The tenth term has x^0y^9.


The term number k leads to the y having an exponent of k-1.


Therefore, the 7th term will have y^(7-1) = y^6 involved. This immediately leads to x^3
So we have x^3y^6 as the entire variable term.
Note the exponents add to n = 9.


The coefficient is found by looking at the 7th item in the row 1,9,36,... in Pascal's Triangle. That value is 84.
Alternatively, use the nCr combination formula with n = 9 and r = 6. 
We use r = 6 instead of r = 7 because the count starts at r = 0. Meaning r = 6 is the 7th term.


Therefore, we end up with 84x^3y^6 as the 7th term of (x+y)^9.
Use software like WolframAlpha to confirm this.


Answer: Choice A
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