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In Problems 57– 80, solve each equation on the interval 0≤θ≤2π.

cos2θ-sin2θ+sinθ=0

Short Answer

Expert verified

The solution set of the given equation is7Ï€6,11Ï€6,Ï€2

Step by step solution

01

Step 1. Given Information 

In the given problems we have to solve each equation on the interval 0≤θ≤2π.

cos2θ-sin2θ+sinθ=0

02

Step 2. The equation in its present form contains a cosine and sine. 

However, a form of the Pythagorean Identity, sin2θ+cos2θ=1, can be used to transform the equation into an equivalent one containing only cosines.

cos2θ-sin2θ+sinθ=0(1-sin2θ)-sin2θ+sinθ=01-sin2θ-sin2θ+sinθ=01-2sin2θ+sinθ=0-2sin2θ+sinθ+1=0-(2sin2θ-sinθ-1)=02sin2θ-sinθ-1=0

03

Step 3. Now factor the equation.

2sin2θ-(2-1)sinθ-1=02sin2θ-2sinθ+sinθ-1=02sinθ(sinθ-1)+1(sinθ-1)=0(2sinθ+1)(sinθ-1)=0

Use the Zero-Product Property.

role="math" localid="1646929056145" 2sinθ+1=0orsinθ-1=02sinθ+1-1=0-1orsinθ-1+1=0+12sinθ=-1orsinθ=122sinθ=-12orsinθ=1sinθ=-12orsinθ=1

04

Step 4. Solving each equation in the interval [0,2π), we obtain 

θ=7π6,11π6orθ=π2

So the solution set is7Ï€6,11Ï€6,Ï€2.

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