Question

)
If 3tan AtanB = 1 then 2cos(A+B) =
A) cos(B-A)
B) sin(A+B)
C) sin(A-B)
D) none​

Answer 1

Answer:

3 tan A tanB = 1

3 sinAsinB/cosAcosB = 1

3sinAsinB = cosAcosB

2 sinAsinB = cosAcosB - sinAsinB

=> cos(A+B) = 2sinAsinB

=> 2cos(A+B) = 4sinAsinB

(D) none