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91Ó°ÊÓ

Solve the equation on the interval 0≤θ≤2π.

4sin2θ=1+4cosθ

Short Answer

Expert verified

On solving the equation, we get,

θ∈π3,5π3

Step by step solution

01

Step 1. Given information.

Consider the given question,

4sin2θ=1+4cosθ0≤θ≤2π

We know, sin2θ=1-cos2θ,

41-cos2θ=1+4cosθ4-4cos2θ=1+4cosθ4cos2θ+4cosθ+3=02cosθ-12cosθ+3=0

Then,

localid="1646749506085" 2cosθ-1=0cosθ=12

Also,

2cosθ+3=0cosθ=-32

This equation is invalid as cosine value must lie within the range-1,1.

02

Step 2. Solve the equation for the given interval.

Consider the given question,

cosθ=120≤θ≤2π

Solving cosθ=12for the given interval,

cosθ=12θ=cos-112θ=π3,5π3

Therefore, the solution set is θ∈π3,5π3.

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