Question

find the value of sin 15° hence deduce the value of cos 75°​

Answer 1

Step-by-step explanation:

You can write cos 75= cos (45+30)

Now cos (a+b)= cos a*cos b-sin a* sin b

So,

cos (45+30)=cos 45*cos 30- sin 45* sin 30

You know the value of cos45 sin45 cos 30 and sin 30

So cos (45+30)={(1/sqrt 2)*(sqrt 3/2)-(1/sqrt 2)* 1/2)}