Find the two middle terms of (a - 2b)⁷. Give the coefficient of each.

Step 1. Which terms. $n = 7$, so the middle terms are $T_4$ and $T_5$.

Step 2. The $4$th term. $T_4 = {}^7C_3\,a^4(-2b)^3 = 35 \times (-8)\,a^4b^3 = -280a^4b^3$.

Step 3. The $5$th term. $T_5 = {}^7C_4\,a^3(-2b)^4 = 35 \times 16\,a^3b^4 = 560a^3b^4$.