Q. b) Find the general solution of cosθ+Cos3θ+cos5θ=0ORProve that: tan−1x−tan−1y=tan−11+xyx−y
Apply sum-to-product identities: Use the sum-to-product identities to simplify cosθ+cos5θ.cosθ+cos5θ=2⋅cos(2θ+5θ)⋅cos(2θ−5θ)= 2⋅cos(3θ)⋅cos(−2θ)= 2⋅cos(3θ)⋅cos(2θ)
Factor out cos(3θ): Now we have 2×cos(3θ)×cos(2θ)+cos(3θ). Factor out cos(3θ). cos(3θ)×(2×cos(2θ)+1)
Find general solution: Set the equation equal to zero to find the general solution. cos(3θ)⋅(2⋅cos(2θ)+1)=0
Solve for cos(3θ): Solve for when each factor is equal to zero.For cos(3θ)=0, the general solution is:3θ=(2n+1)⋅2π, where n is an integer.θ=(2n+1)⋅6π
Solve for cos(2θ): For 2⋅cos(2θ)+1=0, solve for cos(2θ).cos(2θ)=−212θ=±(2n+1)⋅3π, where n is an integer.θ=±(2n+1)⋅6π
Combine solutions: Combine the solutions for θ.θ=(2n+1)×6π and θ=±(2n+1)×6π