Розділ 3. КООРДИНАТИ І ВЕКТОРИ » 14.9-10
(c ⃗; d ⃗) = φ. Знайдіть c ⃗ ● d ⃗, якщо: 1) |c ⃗| = 5, |d ⃗| = 1; φ = 0°; c ⃗ • d ⃗ = 5 • 1•cos 0° = 5 • 1 = 5. 2) |c ⃗| = 4; |d ⃗| = 7; φ = 45°. c ⃗ • d ⃗ = 4 • 7 • √2/2 = 14√2. 3) |c ⃗| = 2, |d ⃗| = 1, φ = 120°. c ⃗ • d ⃗ = 2 • cos 120° = 2 • (–1/2) = –1. 4) |c ⃗| = 7, |d ⃗| = 6; φ = 150°; c ⃗ • d ⃗ = 7 • 6 • cos 150° = 42 • (–√3/2) = –21√3.