SOLUTION: Find the fifth term of (7x+2y)^15 This is what I have so far. (n) (r) (a)^n-r(b)^r a=7 b=2 n=15 r=4 15 nCR 4*(7)^11*(2)^4 The answer that the calculator gives y

Algebra ->  Permutations -> SOLUTION: Find the fifth term of (7x+2y)^15 This is what I have so far. (n) (r) (a)^n-r(b)^r a=7 b=2 n=15 r=4 15 nCR 4*(7)^11*(2)^4 The answer that the calculator gives y      Log On


   

Question 379247: Find the fifth term of (7x+2y)^15
This is what I have so far.
(n)
(r) (a)^n-r(b)^r
a=7
b=2
n=15
r=4
15 nCR 4*(7)^11*(2)^4
The answer that the calculator gives you is 4.32^13. I am confused about what exponents I put for x and y since the solution of the equation has an exponent involved with it. Any help would be appreciated. Thanks!
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
To know the 5th term (starting from the LEFT), you must realize that counting of powers of 2y start at 0 (from the very first term, again from the left). Hence at the 5th term, the power of 2y must be 4.
This is your r in nCr. Thus by the binomial theorem, the 5th term must be