Question

If sin A=4/5 and cos B=-12/13,
where A and B lie in first and third quadrant respectively, then
cos(A + B) =

Answer 1

Answer:

Step-by-step explanation:

3,4,5 are Pythagoras triple

sin A =4/5

cos A=adj/hyp=3/5

5,12,13 are Pythagoras triple

cos B=12/13

sin B=opp/hyp=5/13

cos(A+B)=cos Acos B-sin Asin B

=(3/5×12/13)-(4/5×5/13)

=36/65-4/13

=16/65