Question

Evaluate cos 195° for the answer above.​

Answer 1

Answer:

Step-by-step explanation

first   cos 15 = cos [45-30] =cos45cos30 +sin45sin30

=[1/√2][√3/2]  + [1/2][1/√2]  =[√3+1]/2√2

now cos 195 = cos[180 +15] = - cos 15 = -[√3+1]/2√2

formua used

cos[A-B] =cosAcosB +sinAsinB

COS[180+ A] = - cos A