Answer :

cos 40° + cos 80° + cos 160° + cos 240°


= (cos 40° + cos 80°) + (cos 160° + cos 240°)


= 2 + 2


= 2cos 60° cos 20° + 2cos 200° cos 40°


= 2 1/2 cos 20° + 2cos (180 + 20)° cos 40°


= cos 20° - 2cos 20° cos 40°


= cos 20° - (cos (40° + 20°) + cos (40° - 20°))


= cos 20° - (cos 60° + cos 20°)


= - cos 60°


= - 1/2 (Ans)

Rate this question :

How useful is this solution?
We strive to provide quality solutions. Please rate us to serve you better.
Try our Mini CourseMaster Important Topics in 7 DaysLearn from IITians, NITians, Doctors & Academic Experts
Dedicated counsellor for each student
24X7 Doubt Resolution
Daily Report Card
Detailed Performance Evaluation
caricature
view all courses
RELATED QUESTIONS :

Prove that :
<
RD Sharma - Mathematics

Prove that:
</
RD Sharma - Mathematics

Prove that:
</
RD Sharma - Mathematics

Prove that :
<
RD Sharma - Mathematics

Prove that:
</
RD Sharma - Mathematics

Prove that:
</
RD Sharma - Mathematics

Prove that:
</
RD Sharma - Mathematics

Prove that:
</
RD Sharma - Mathematics

Prove that:
</
RD Sharma - Mathematics

Prove that:
</
RD Sharma - Mathematics