Find the middle term in the expansion of (3x − x³/6)⁷.

Clearly, the given expansion contains 8 terms.

∴ Middle terms are (8/2)^th and ((8/2) + 1)^th term, i.e., 4th and 5th terms.

Now,

T₄ = T₃₊₁ = (−1)³ × ⁷C₃ × (3x)⁷⁻³ × (x³/6)³

= −35 × 81 × x⁴ × x⁹ / 216 = −105x¹³ / 8

And

T₅ = T₄₊₁ = (−1)⁴ × ⁷C₄ × (3x)⁷⁻⁴ × (x³/6)⁴

= 35 × 27 × x³ × x¹² / 1296 = 35x¹⁵ / 48

Hence, the middle terms are −105x¹³ / 8 and 35x¹⁵ / 48.