Question

cos85°+cos155°+cos35°=​

Answer 1

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

if satisfied then mark it as branliest answer...

Answer 2

Correct question:-

Prove that Cos45° + cos 115° + Cos35° = 0

Answer:(this answer is verified)

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)