tolong bantuin. tentukan cos gamma

TriGonoMetRi

tan a = 0,75 = 3/4
triple Pythagoras : 3,4,5
sin a = 3/5
cos a = 4/5

cos b = 5/13
triple Pythagoras : 5,12,13
sin b = 12/13

gamma = c
a + b + c = 180°
c = 180° - (a + b)

cos c
= cos (180° - (a + b))
= - cos (a + b)
= sin a sin b - cos a cos b
= 3/5 . 12/13 - 4/5 . 5/13
= (36 - 20)/65
= 16/65