Відповіді до вправ: 16.24

16.24 (a, b) = 120°, |a| = 2, |b| = 3. Знайдіть:

(a, b) = 120°; |a| = 2; |b| = 3.

1) a • b = |a| |b| • cos∠(a, b) = 2 • 3 • cos120° = 2 • 3 • (–12) = –3.

2) (a + b) • a = a² + b • a = 2² – 3 = 1.

3) b(a – b) = ba – b² = –3 – 3² = –3 –9 = –12.

4) a(2a – 3b) = 2a² – 3ab = 2 • 4 – 3 • (–3) = 8 + 9 = 17.