Question

Ma ajuta si pe mine cineva ? Sa se calculeze cos ( a+b ) , cos ( a-b ) daca : 
 Sin a = 3/5 , sin b = 5/13 , a,b ∈ ( 0 , π/2 ) .

Answer 1

sin <a+sin<b=3/5 +5/13=   39+65/65=104/65
cos (a+b)=1/sin(a+b)= 1 supra 104/65= 65/104
cos(a-b)=1/sin(a-b)=1 supra 39-65/65=  1 supra -26/65=  - 65/26= -5/2