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The best way to learn this is to multiply out the terms of (d – 4b)^3. First do (d – 4b)^2, then multiply that by (d – 4b). Collect all the terms that have the same powers of d and b. Then arrange them by decreasing powers of d.
First 2 terms are d^3 and - 3d^2(4b)
(d - 4b)³ = (3C0)(-4b)³ + (3C1)(d)(-4b)² + (3C2)(d²)(-4b) + (3C3)(d³)
= -64b³ + 48d(b²) - 12(d²)b + d³