Question

Use the formula to expand:

(7) (–5a + 4b – 3c)²

Answer 1

We know that (x + y + z)² = x² + y² + z² + 2xy + 2yz + 2xz
Comparing (–5a + 4b – 3c)² with (x +y + z)² , we get:
x = –5a, y = 4b and z = –3c
Substituting these in the above formula:
(–5a + 4b – 3c)² = (–5a)² + (4b)² + (–3c)² + 2 × (–5a) × (4b) + 2 × (4b) × (–3c) + 2 × (–3c) × (–5a)
= 25a² + 16b² + 9c² – 40ab – 24bc + 30ac