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Popular Trigonometry >

0=sin(θ/2)-sin(θ)

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Solution

0=sin(2θ​)−sin(θ)

Solution

θ=32π​+38πn​,θ=2π+38πn​,θ=8πn,θ=4π+8πn
+1
Degrees
θ=120∘+480∘n,θ=360∘+480∘n,θ=0∘+1440∘n,θ=720∘+1440∘n
Solution steps
0=sin(2θ​)−sin(θ)
Switch sidessin(2θ​)−sin(θ)=0
Rewrite using trig identities
sin(2θ​)−sin(θ)
Use the Sum to Product identity: sin(s)−sin(t)=2sin(2s−t​)cos(2s+t​)=2sin(22θ​−θ​)cos(22θ​+θ​)
Simplify 2sin(22θ​−θ​)cos(22θ​+θ​):−2cos(43θ​)sin(4θ​)
2sin(22θ​−θ​)cos(22θ​+θ​)
22θ​−θ​=−4θ​
22θ​−θ​
Join 2θ​−θ:−2θ​
2θ​−θ
Convert element to fraction: θ=2θ2​=2θ​−2θ⋅2​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2θ−θ⋅2​
Add similar elements: θ−2θ=−θ=2−θ​
Apply the fraction rule: b−a​=−ba​=−2θ​
=2−2θ​​
Apply the fraction rule: b−a​=−ba​=−22θ​​
Apply the fraction rule: acb​​=c⋅ab​22θ​​=2⋅2θ​=−2⋅2θ​
Multiply the numbers: 2⋅2=4=−4θ​
=2sin(−4θ​)cos(22θ​+θ​)
Use the negative angle identity: sin(−x)=−sin(x)=2cos(22θ​+θ​)(−sin(4θ​))
Remove parentheses: (−a)=−a=−2cos(22θ​+θ​)sin(4θ​)
22θ​+θ​=43θ​
22θ​+θ​
Join 2θ​+θ:23θ​
2θ​+θ
Convert element to fraction: θ=2θ2​=2θ​+2θ⋅2​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2θ+θ⋅2​
Add similar elements: θ+2θ=3θ=23θ​
=223θ​​
Apply the fraction rule: acb​​=c⋅ab​=2⋅23θ​
Multiply the numbers: 2⋅2=4=43θ​
=−2cos(43θ​)sin(4θ​)
=−2cos(43θ​)sin(4θ​)
−2cos(43θ​)sin(4θ​)=0
Solving each part separatelycos(43θ​)=0orsin(4θ​)=0
cos(43θ​)=0:θ=32π​+38πn​,θ=2π+38πn​
cos(43θ​)=0
General solutions for cos(43θ​)=0
cos(x) periodicity table with 2πn cycle:
x06π​4π​3π​2π​32π​43π​65π​​cos(x)123​​22​​21​0−21​−22​​−23​​​xπ67π​45π​34π​23π​35π​47π​611π​​cos(x)−1−23​​−22​​−21​021​22​​23​​​​
43θ​=2π​+2πn,43θ​=23π​+2πn
43θ​=2π​+2πn,43θ​=23π​+2πn
Solve 43θ​=2π​+2πn:θ=32π​+38πn​
43θ​=2π​+2πn
Multiply both sides by 4
43θ​=2π​+2πn
Multiply both sides by 444⋅3θ​=4⋅2π​+4⋅2πn
Simplify
44⋅3θ​=4⋅2π​+4⋅2πn
Simplify 44⋅3θ​:3θ
44⋅3θ​
Multiply the numbers: 4⋅3=12=412θ​
Divide the numbers: 412​=3=3θ
Simplify 4⋅2π​+4⋅2πn:2π+8πn
4⋅2π​+4⋅2πn
4⋅2π​=2π
4⋅2π​
Multiply fractions: a⋅cb​=ca⋅b​=2π4​
Divide the numbers: 24​=2=2π
4⋅2πn=8πn
4⋅2πn
Multiply the numbers: 4⋅2=8=8πn
=2π+8πn
3θ=2π+8πn
3θ=2π+8πn
3θ=2π+8πn
Divide both sides by 3
3θ=2π+8πn
Divide both sides by 333θ​=32π​+38πn​
Simplifyθ=32π​+38πn​
θ=32π​+38πn​
Solve 43θ​=23π​+2πn:θ=2π+38πn​
43θ​=23π​+2πn
Multiply both sides by 4
43θ​=23π​+2πn
Multiply both sides by 444⋅3θ​=4⋅23π​+4⋅2πn
Simplify
44⋅3θ​=4⋅23π​+4⋅2πn
Simplify 44⋅3θ​:3θ
44⋅3θ​
Multiply the numbers: 4⋅3=12=412θ​
Divide the numbers: 412​=3=3θ
Simplify 4⋅23π​+4⋅2πn:6π+8πn
4⋅23π​+4⋅2πn
4⋅23π​=6π
4⋅23π​
Multiply fractions: a⋅cb​=ca⋅b​=23π4​
Multiply the numbers: 3⋅4=12=212π​
Divide the numbers: 212​=6=6π
4⋅2πn=8πn
4⋅2πn
Multiply the numbers: 4⋅2=8=8πn
=6π+8πn
3θ=6π+8πn
3θ=6π+8πn
3θ=6π+8πn
Divide both sides by 3
3θ=6π+8πn
Divide both sides by 333θ​=36π​+38πn​
Simplifyθ=2π+38πn​
θ=2π+38πn​
θ=32π​+38πn​,θ=2π+38πn​
sin(4θ​)=0:θ=8πn,θ=4π+8πn
sin(4θ​)=0
General solutions for sin(4θ​)=0
sin(x) periodicity table with 2πn cycle:
x06π​4π​3π​2π​32π​43π​65π​​sin(x)021​22​​23​​123​​22​​21​​xπ67π​45π​34π​23π​35π​47π​611π​​sin(x)0−21​−22​​−23​​−1−23​​−22​​−21​​​
4θ​=0+2πn,4θ​=π+2πn
4θ​=0+2πn,4θ​=π+2πn
Solve 4θ​=0+2πn:θ=8πn
4θ​=0+2πn
0+2πn=2πn4θ​=2πn
Multiply both sides by 4
4θ​=2πn
Multiply both sides by 444θ​=4⋅2πn
Simplifyθ=8πn
θ=8πn
Solve 4θ​=π+2πn:θ=4π+8πn
4θ​=π+2πn
Multiply both sides by 4
4θ​=π+2πn
Multiply both sides by 444θ​=4π+4⋅2πn
Simplifyθ=4π+8πn
θ=4π+8πn
θ=8πn,θ=4π+8πn
Combine all the solutionsθ=32π​+38πn​,θ=2π+38πn​,θ=8πn,θ=4π+8πn

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Frequently Asked Questions (FAQ)

  • What is the general solution for 0=sin(θ/2)-sin(θ) ?

    The general solution for 0=sin(θ/2)-sin(θ) is θ=(2pi)/3+(8pin)/3 ,θ=2pi+(8pin)/3 ,θ=8pin,θ=4pi+8pin
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