Download the app

Questions  

The possible values of θ(0,π) such that sin(θ)+sin(4θ)+sin(7θ)=0 are

a
π4,5π12,π12,2π3,3π4,8π9
b
2π9,π4,π2,2π3,3π4,35π36
c
2π9,π4,π2,2π3,3π4,8π9
d
2π9,π4,4π9,π2,3π4,8π9

detailed solution

Correct option is D

sin⁡θ+sin⁡4θ+sin⁡7θ=0⇒ 2sin⁡4θcos⁡3θ+sin⁡4θ=0⇒ sin⁡4θ(2cos⁡3θ+1)=0⇒ sin⁡4θ=0 or cos⁡3θ=−1/2=cos⁡(2π/3)⇒ θ=π4,π2,3π4 or 3θ=2π/3, 2π 2π/3⇒ θ=2π9,π4,π2,4π9,3π4,8π9

Talk to our academic expert!

+91

Are you a Sri Chaitanya student?


Similar Questions

If cosA+cosB=m and sinA+sinB=n where m,n0, then sin(A+B) is equal to


phone icon
whats app icon