pada segitiga abc sisi a=7 b=3 c=5 baerapa nilai sin alpha

a²= b²+c²- 2bc cos Alpha
49= 9+25-30 cos alpha
cos alpha = 34-49/30=-15/30
= -1/2
maka sisi miring = 2
sisi depan = √4-1= √3
jadi sin alpha = depan/ miring = √3/2= 1/2√3

Bab Trigonometri
Matematika SMA Kelas X

cos a = (b² + c² - a²) / (2 x b x c)
cos a = (3² + 5² - 7²) / (2 x 3 x 5)
cos a = (9 + 25 - 49) / 30
cos a = -15/30
cos a = - 1/2

sin a = √(1 - cos² a)
sin a = √(1 - (-1/2)²)
sin a = √(1 - 1/4)
sin a = √((4 - 1)/4)
sin a = √(3/4)
sin a = (1/2) √3