Вправи: 534

534. Знайдіть:

1) ab = |a||b| cos 45° = 2 • 1 • 22 = 2;

2) a(a + b) = a² + ab = |a|² + ab = 2² + 2 = 4 + 2;

3) b(a – b) = ab – |b|² = 2 – 1;

4) a(2a + 5b) = 2a² + 5ab = 2|a|² + 5ab = 2 • 2² + 52 = 8 + 52.