Question

Fie a,b€(0;π/2) a.î. sin a=3/5 si cos b =12/13. Sa se calc. cos(a-b)

Answer 1

cos a=√1-sin²a= √1-9/25= 4/5
sin b= √1-cos²b= √1-144/169= 5/13

cos(a-b)= cos a cosb+ sina sin b= 4/5*12/13 + 3/5*5/13= (48+15)/5*13= 63/65

O seara buna!