Відповіді АЛГЕБРА: 15.13-14

15.13

1) sin105°sin15° = 12(cos90° – cos120°) = 12(0 + cos60°) = 12 • 12 = 14

2) cos15° • sin75° = 12(sin90° + sin60°) = 12(1 + 32) = 12 + 34

15.14

1) cos75°cos105° = 12(cos30° + cos180°) = 12(32 – 1) = 34 – 12

2) sin15°cos105° = 12(cos120° + sin(–90°)) = 12(–cos60° – sin90°) =

= 12(–12 – 1) = –34