wiz-icon
MyQuestionIcon
MyQuestionIcon
1
You visited us 1 times! Enjoying our articles? Unlock Full Access!
Question

If cosα+cosβ=a,sinα+sinβ=b and αβ=2θ then cos3θcosθ is equal to

A
a2+b22
No worries! We‘ve got your back. Try BYJU‘S free classes today!
B
a2+b23
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
C
3a2b2
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
(a2+b2)4
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution

The correct option is C a2+b23
Given cosα+cosβ=a ....(1)
sinα+sinβ=b ....(2)
Squaring and adding (1) and (2), we get
2+2cos(αβ)=a2+b2
4cos2θ=a2+b2 ....(3)
Consider,
cos3θcosθ
=4cos3θ3cosθcosθ
=a2+b23 (using 3)

flag
Suggest Corrections
thumbs-up
0
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
Transformations
MATHEMATICS
Watch in App
Join BYJU'S Learning Program
CrossIcon