## (Math Quiz 10 – CT) In the expansion ({left( {2a – b} right)^5}), the coefficient of the 3rd term is equal to:

• Question:

In the expansion $${\left( {2a – b} \right)^5}$$, the coefficient of the third term is equal to:

Reference explanation:

We have: $${\left( {2a – b} \right)^5}$$
$$= C_5^0{\left( {2a} \right)^5} – C_5^1{\left( {2a} \right)^4}b + C_5^2{\left( {2a} \right )^3}{b^2} \ldots$$
Therefore the coefficient of the third term is equal to $$C_5^2.8 = 80$$.