What is the fourth term in the expansion of #(2x-y)^5#?

1 Answer
Noah G
Feb 13, 2016

You can find this by using the formula #t_(r + 1) =_nC_r xx a^(n - r) xx b^r#

Explanation:

r can be found by solving the simple equation #t_(r + 1) = 4# We can immediately eliminate the t, and we find that r is 3. n is the exponent, which is 5 in this case. Note the n and the r are in base at the C.

#t_4 =_5C_3 xx 2x^(5 - 3) xx -y^3#

#t_4 = 10 xx 4x^2(-y^3)#

#t_4 = -40x^2y^3#

Your fourth term is #-40x^2y^3#.

Practice exercises:

  1. Find the 7th term in #(-2x + 3y)^12#

  2. Find the middle term of #(3x - y^3)^8#

Good luck!

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