tolong dibantu no. 11 dan 12 soal mtk minat trigonometri lanjutan kelas 11

itu dikali ya?

11. 2/3 sin(15)sin(285)=-1/3[cos(300)-cos(270)]=-1/3[cos(270+30)-0]=-1/3*(sin(30))=-1/3*(1/2)=-1/6

12. sin(7,5)sin(127,5)=-1/2*[cos(135)-cos(120)]=-1/2*[cos(180-45)-cos(180-60)]=-1/2*[-cos(45)+cos(60)]=-1/2*[-akar(2)/2+1/2]=1/4*[akar(2)-1]

Trigonometri

11)
2/3  sin 15° sin 285 =
= -1/3  (- 2 sin 285 sin 15)
= - 1/3 { cos (285+15) - cos (285-15)}
= - 1/3 { cos 300 - cos 270 }
= - 1/3  { cos (360 -60) - cos (360-90)}
= -1/3  { cos 60 - cos 90 }
= - 1/3 ( 1/2 - 0)
= - 1/6

12)
sin 7,5 cos 127,5 =
= 1/2 { 2 cos 127,5 sin 7,5)
= 1/2  { sin (127,5 +7,5) - sin (127,5 - 7,5)}
= 1/2 { sin 135 - sin 120 }
= 1/2 { sin(180-45) - sin(180-60)}
= 1/2 { sin 45 - sin 60 }
= 1/2 (1/2 √2 - 1/2 √3)
= 1/2 (1/2)(√2 - √3)
= 1/4 (√2 - √3)