What is the 4th term in the expansion (a-2b)^6?

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What is the 4th term in the expansion (a-2b)^6?

2007-02-02 11:47:40 · 2 answers · asked by SICK MY DUCK! 1 in Science & Mathematics ➔ Mathematics

2 answers

20*3*(-2)^3a^3b^3
-480*a^3*b^3

2007-02-02 11:54:37 · answer #1 · answered by bruinfan 7 · 0⤊ 0⤋

Remember, in an expansion of this kind there are seven terms because the powers for a and b range from zero to six. The fourth term in the expansion is:

(6C3)*[(a)^(6-3)]*[(-2b)^3] = (20*1*(-2)Â³)aÂ³bÂ³ = -160aÂ³bÂ³

2007-02-02 20:32:10 · answer #2 · answered by Northstar 7 · 0⤊ 0⤋