diketehui segitiga abc pqnjang sisi a = 8, sisi b =7 dan sisi c =4 , hitunglah besar

a² = b² +c² - 2bc cos A
64 = 49 + 16 - 56 cos A
-1 = -56cos A
cos A = 1/56
A =88,98°

Bab Trigonometri
Matematika SMA Kelas XI

aturan cosinus
cos A = (b² + c² - a²)/(2 x b x c)
cos A = (7² + 4² - 8²)/(2 x 7 x 4)
cos A = (49 + 16 - 64)/56
cos A = 1/56
A = 88,98°