Question

(i)
cos O + cos20 + cos 40 + cos 50
sin 0 + sin 20 + sin 40 + sin 50
= cot 30​

Answer 1

Answer:

Step-by-step explanation:

Given, cos 40 + cos 50 + cos 70 + cos 80

We know that cos a + cos b= 2 cos(a+b)/2 cos(a-b)/2.

        (2 cos(40+80)/2 cos(40-80)/2) + (2 cos (50+70)/2 cos(50-70)/2)

      = 2 cos 60 cos (-20)  + 2 cos 60 cos (-10)

     = 2 * 1/2 * cos 20 + 2 * 1/2 cos 10

     = cos 20 + cos