jika alfa dan beta sudut lancip, cos alfa =4/5, dan sin beta=5/13, tentukan cos(alfa-beta)! pakai cara ya teman tem

jawab
A dan B sudut lancip
cos A = 4/5
sin A = √(1 - cos²A) = √(1 - (4/5)²
sin A = √(1 - 16/25) 
sin A = √(9/25) = 3/5

sin B = 5/13
cos B = √(1 - sin² B) = √(1 - (5/13)²
cos B = √(1 - 25/169)
cos B = √(144/169)
cos B = 12/13

cos (A - B ) =
= cos A cos B + sin A sin B
= (4/5)(12/13) + (3/5)(5/13)
= 48/65  + 15/65
= 63/65