Answer :

We need to find the value of


Let,




Let us find sin a and cos b.


For sin a,


We know the trigonometric identity, sin2 a + cos2 a = 1


sin2 a = 1 – cos2 a


sin a = √(1 – cos2 a)


Substituting the value of cos a,







We have .


So, we can find tan a.





tan a = 7 …(i)


For cos b,


We know the trigonometric identity,


sin2 b + cos2 b = 1


cos2 b = 1 – sin2 b


cos b = √(1 – sin2 b)


Substituting the value of sin b,






We have .


So, we can find tan b.





tan b = 4 …(ii)


We can write as,



Now, we need to solve Right Hand Side (RHS).


We know the trigonometric identity,



Substituting the values of tan a and tan b from (i) and (ii),





So,


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