Please help with this problem.

Question

Cos A+B= -8/17 in quadrant III, Cos B 13/85 Quadrant I. Find Cos A+B

Answer 1

Cos B=13/85 Quadrant I; cos B=.15294..........; B=81.2025..........°

Cos A+B= -8/17 in quadrant III

cos(a+81.2)=-.4705............

cosa+.152.96...........=.4705

cosa=.31764............

a=71.4793+180=251.4793...........°

Cos A+B=cos(251.4793+81.2025)=cos332.6818..........=.88847............

Answer 2

it's in your statement. -8/17