SOLUTION: What is the coefficient of x^2y^5 when (x − 2y)^7 is expanded? Hint: Remember the −2.

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Question 927998: What is the coefficient of x^2y^5 when (x − 2y)^7 is expanded?
Hint: Remember the −2.
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

For the coefficients, use the seventh row of Pascal's triangle , or combinations formula: C(7,n-1)
keep in mind the exponents will have a sum of 7 in each term, and the first factor will decrease in power as the second increases.

Now simplify each term:

so, your coefficient is 21%2A%28-2%29%5E5=21%2A%28-32%29=-672