Question

The value of
cOS 35-
cos 95° + cos 155​

Answer 1

Answer:

o

Step-by-step explanation:

cos 35°+cos85°+cos155°

= 2cos{(35°+85°)/2}cos{(35°-85°)/2}+cos(180°-25°)  

[cosC+cosD=2cos{(C+D)/2}cos{(C-D)/2}]

=2cos(120°/2)cos(50°/2)+cos{(90°×2)-25°}

=2cos60°cos25°+(-cos25°)

=2×(1/2)cos25°-cos25°

=0 (Proved)