§ 20: 20.22

20.22 Знайдіть скалярний добуток (2a – 3b)(a – 2b), якщо a (2; –1;

–2), b (4; –3; 2).

a (2; –1; –2); b (4; –3; 2).

(2a – 3b)(a – 2b) = 2a² – 4ab – 3ab + 6b² = 2 • (2² + (–1)² + (–2)²) – 7 • (2 • 4 + 1 • 3 – 2 • 2) + 6 • (4² + (–3)² + 2²) = 18 – 49 + 174 =

= 143.