Question

sec a=17/8 and cosec b=5/4 then sec(a+b)=??

Answer 1

Sec (A+B) = 1/cos(A+B)
we know that cos(A+B) = Cos A cosB - sinA sinB
Cos A = 8/17; Sin2A + (64/289) = 1 => Sin2A = 225/289; Sin A = 15/17
Sen B = 4/5 ; 16/25 + cos2B = 1 => cos2B = 9/25; cos B = 3/5

With this, we know that cos (A+B) = 36/(17*5) and Sec (A+B)= (85/36)