Simplify the following expression.

$(2a - b - 3c)(4a^2 + b^2 + 9c^2 + 2ab + 6ac - 3bc )$

$8a^3 - b^3 - 27c^3 - 18abc$

Given,

(2a - b - 3c)(4a² + b² + 9c² + 2ab + 6ac - 3bc)

= 8a³+2ab²+18ac²+4a²b+12a²c−6abc−4a²b−b³−9bc²−2ab²−6abc+3b²c−12a²c−3b²c−27c³−6abc−18ac²+9bc²

= 8a³−18abc−b³−27c³

So the value of (2a - b - 3c)(4a² + b² + 9c² + 2ab + 6ac - 3bc) = 8a³−18abc−b³−27c³