Question

Find the 4th term of the expansion of (2a-b)^7

Answer 1

-560a^4b^3 .

Explanation:

For a binomial expansion :

(r + 1)th term of (a + b)^n = nCr a^(n-r) b^r.

So the 4th term of (2a - b)^7

= (3 + 1)th term = 7C3 (2a)^(7-3) (-b)^3

= 35 * 16a^4* -b^3

= -560a^4b^3 (answer).