Вправи: 51

51. Обчисліть:

1 ) cos²150° – sin²150° + tg135° = (–cos² 30°) – sin² 60° – tg 45° =

= (–32)² – (32)² – 1 = 34 – 34 – 1 = –1;

2) tg 120° • cos 120° + sin 120° = sin120°cos120° • cos120° + sin 120°=

= sin 120° + sin 120° = 2sin 120° = 2sin(180° – 60°) = 2 • sin 60°=

= 232 = 3.