Answer 1

(2x + 3y + 4z)²

(a + b + c)² ≡ a² + b² + c² + 2ab + 2bc + 2ca

∴ (2x + 3y + 4z)² = (2x)² + (3y)² + (4z)² + 2(2x)(3y) + 2(3y)(4z) + 2(4z)(2x)

= 4x² + 9y² + 16z² + 12xy + 24yz + 16zx