Question

Find the value of cos (-870°)​

Answer 1

Step-by-step explanation:

here is the answer.. solve it..

Answer 2

SOLUTION:-

•Since the given angle (-870°) has negative sign, we have to assume it falls in the fourth quadrant.

In the fourth quadrant, "cos" is positive. 

So, we have cos (-870°)  =  cos 870°.

The given 870° is greater than 360°.

So, we have to divide 870 by 360 and take the remainder. 

When 870 is divided by 360, the remainder is 150. 

Therefore,

870°  =  150°

Then,

cos 870°  =  cos 150° 

cos 870°  =  cos (180° - 30°)

cos 870°  =  - cos 30°

cos 870  =  - √3/2