Question

29. If sina
-15
and tanb
= 1, then the value of cos(a + b) is
a. 3
b. X
C 2
d. 0
​

Answer 1

Answer :

I am not Getting i guess there is some mistake in question

By my understanding i Got an answer which you can see

Explanation :

Sin (a - 15)° = 1  & tan b = 1

Sin 90° = 1       &  tan 45° = 1

  (a-15) =  90°                      ⇒   b = 45°

  ⇒ a = 105°

Asking for cos(a +b)

                 = cos(105°+45°)

                 = cos150°

                  = -√3/2