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Popular Trigonometry >

2-2cos^2(x)=2sin^2(x/2)

  • Pre Algebra
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Solution

2−2cos2(x)=2sin2(2x​)

Solution

x=38πn​,x=34π​+38πn​,x=32π​+38πn​,x=2π+38πn​
+1
Degrees
x=0∘+480∘n,x=240∘+480∘n,x=120∘+480∘n,x=360∘+480∘n
Solution steps
2−2cos2(x)=2sin2(2x​)
Subtract 2sin2(2x​) from both sides2−2cos2(x)−2sin2(2x​)=0
Rewrite using trig identities
2−2cos2(x)−2sin2(2x​)
Use the Pythagorean identity: cos2(x)+sin2(x)=1cos2(x)=1−sin2(x)=2−2(1−sin2(x))−2sin2(2x​)
Simplify 2−2(1−sin2(x))−2sin2(2x​):2sin2(x)−2sin2(2x​)
2−2(1−sin2(x))−2sin2(2x​)
Expand −2(1−sin2(x)):−2+2sin2(x)
−2(1−sin2(x))
Apply the distributive law: a(b−c)=ab−aca=−2,b=1,c=sin2(x)=−2⋅1−(−2)sin2(x)
Apply minus-plus rules−(−a)=a=−2⋅1+2sin2(x)
Multiply the numbers: 2⋅1=2=−2+2sin2(x)
=2−2+2sin2(x)−2sin2(2x​)
2−2=0=2sin2(x)−2sin2(2x​)
=2sin2(x)−2sin2(2x​)
−2sin2(2x​)+2sin2(x)=0
Factor −2sin2(2x​)+2sin2(x):2(sin(x)+sin(2x​))(sin(x)−sin(2x​))
−2sin2(2x​)+2sin2(x)
Factor out common term 2=2(−sin2(2x​)+sin2(x))
Factor sin2(x)−sin2(2x​):(sin(x)+sin(2x​))(sin(x)−sin(2x​))
sin2(x)−sin2(2x​)
Apply Difference of Two Squares Formula: x2−y2=(x+y)(x−y)sin2(x)−sin2(2x​)=(sin(x)+sin(2x​))(sin(x)−sin(2x​))=(sin(x)+sin(2x​))(sin(x)−sin(2x​))
=2(sin(x)+sin(2x​))(sin(x)−sin(2x​))
2(sin(x)+sin(2x​))(sin(x)−sin(2x​))=0
Solving each part separatelysin(x)+sin(2x​)=0orsin(x)−sin(2x​)=0
sin(x)+sin(2x​)=0:x=2π+8πn,x=6π+8πn,x=38πn​,x=34π​+38πn​
sin(x)+sin(2x​)=0
Rewrite using trig identities
sin(2x​)+sin(x)
Use the Sum to Product identity: sin(s)+sin(t)=2sin(2s+t​)cos(2s−t​)=2sin(22x​+x​)cos(22x​−x​)
Simplify 2sin(22x​+x​)cos(22x​−x​):2cos(4x​)sin(43x​)
2sin(22x​+x​)cos(22x​−x​)
22x​+x​=43x​
22x​+x​
Join 2x​+x:23x​
2x​+x
Convert element to fraction: x=2x2​=2x​+2x⋅2​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2x+x⋅2​
Add similar elements: x+2x=3x=23x​
=223x​​
Apply the fraction rule: acb​​=c⋅ab​=2⋅23x​
Multiply the numbers: 2⋅2=4=43x​
=2sin(43x​)cos(22x​−x​)
22x​−x​=−4x​
22x​−x​
Join 2x​−x:−2x​
2x​−x
Convert element to fraction: x=2x2​=2x​−2x⋅2​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2x−x⋅2​
Add similar elements: x−2x=−x=2−x​
Apply the fraction rule: b−a​=−ba​=−2x​
=2−2x​​
Apply the fraction rule: b−a​=−ba​=−22x​​
Apply the fraction rule: acb​​=c⋅ab​22x​​=2⋅2x​=−2⋅2x​
Multiply the numbers: 2⋅2=4=−4x​
=2sin(43x​)cos(−4x​)
Use the negative angle identity: cos(−x)=cos(x)=2cos(4x​)sin(43x​)
=2cos(4x​)sin(43x​)
2cos(4x​)sin(43x​)=0
Solving each part separatelycos(4x​)=0orsin(43x​)=0
cos(4x​)=0:x=2π+8πn,x=6π+8πn
cos(4x​)=0
General solutions for cos(4x​)=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​​​​
4x​=2π​+2πn,4x​=23π​+2πn
4x​=2π​+2πn,4x​=23π​+2πn
Solve 4x​=2π​+2πn:x=2π+8πn
4x​=2π​+2πn
Multiply both sides by 4
4x​=2π​+2πn
Multiply both sides by 444x​=4⋅2π​+4⋅2πn
Simplify
44x​=4⋅2π​+4⋅2πn
Simplify 44x​:x
44x​
Divide the numbers: 44​=1=x
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
x=2π+8πn
x=2π+8πn
x=2π+8πn
Solve 4x​=23π​+2πn:x=6π+8πn
4x​=23π​+2πn
Multiply both sides by 4
4x​=23π​+2πn
Multiply both sides by 444x​=4⋅23π​+4⋅2πn
Simplify
44x​=4⋅23π​+4⋅2πn
Simplify 44x​:x
44x​
Divide the numbers: 44​=1=x
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
x=6π+8πn
x=6π+8πn
x=6π+8πn
x=2π+8πn,x=6π+8πn
sin(43x​)=0:x=38πn​,x=34π​+38πn​
sin(43x​)=0
General solutions for sin(43x​)=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​​​
43x​=0+2πn,43x​=π+2πn
43x​=0+2πn,43x​=π+2πn
Solve 43x​=0+2πn:x=38πn​
43x​=0+2πn
0+2πn=2πn43x​=2πn
Multiply both sides by 4
43x​=2πn
Multiply both sides by 444⋅3x​=4⋅2πn
Simplify3x=8πn
3x=8πn
Divide both sides by 3
3x=8πn
Divide both sides by 333x​=38πn​
Simplifyx=38πn​
x=38πn​
Solve 43x​=π+2πn:x=34π​+38πn​
43x​=π+2πn
Multiply both sides by 4
43x​=π+2πn
Multiply both sides by 444⋅3x​=4π+4⋅2πn
Simplify3x=4π+8πn
3x=4π+8πn
Divide both sides by 3
3x=4π+8πn
Divide both sides by 333x​=34π​+38πn​
Simplifyx=34π​+38πn​
x=34π​+38πn​
x=38πn​,x=34π​+38πn​
Combine all the solutionsx=2π+8πn,x=6π+8πn,x=38πn​,x=34π​+38πn​
sin(x)−sin(2x​)=0:x=32π​+38πn​,x=2π+38πn​,x=8πn,x=4π+8πn
sin(x)−sin(2x​)=0
Rewrite using trig identities
−sin(2x​)+sin(x)
Use the Sum to Product identity: sin(s)−sin(t)=2sin(2s−t​)cos(2s+t​)=2sin(2x−2x​​)cos(2x+2x​​)
Simplify 2sin(2x−2x​​)cos(2x+2x​​):2sin(4x​)cos(43x​)
2sin(2x−2x​​)cos(2x+2x​​)
2x−2x​​=4x​
2x−2x​​
Join x−2x​:2x​
x−2x​
Convert element to fraction: x=2x2​=2x⋅2​−2x​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2x⋅2−x​
Add similar elements: 2x−x=x=2x​
=22x​​
Apply the fraction rule: acb​​=c⋅ab​=2⋅2x​
Multiply the numbers: 2⋅2=4=4x​
=2sin(4x​)cos(2x+2x​​)
2x+2x​​=43x​
2x+2x​​
Join x+2x​:23x​
x+2x​
Convert element to fraction: x=2x2​=2x⋅2​+2x​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2x⋅2+x​
Add similar elements: 2x+x=3x=23x​
=223x​​
Apply the fraction rule: acb​​=c⋅ab​=2⋅23x​
Multiply the numbers: 2⋅2=4=43x​
=2sin(4x​)cos(43x​)
=2sin(4x​)cos(43x​)
2cos(43x​)sin(4x​)=0
Solving each part separatelycos(43x​)=0orsin(4x​)=0
cos(43x​)=0:x=32π​+38πn​,x=2π+38πn​
cos(43x​)=0
General solutions for cos(43x​)=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​​​​
43x​=2π​+2πn,43x​=23π​+2πn
43x​=2π​+2πn,43x​=23π​+2πn
Solve 43x​=2π​+2πn:x=32π​+38πn​
43x​=2π​+2πn
Multiply both sides by 4
43x​=2π​+2πn
Multiply both sides by 444⋅3x​=4⋅2π​+4⋅2πn
Simplify
44⋅3x​=4⋅2π​+4⋅2πn
Simplify 44⋅3x​:3x
44⋅3x​
Multiply the numbers: 4⋅3=12=412x​
Divide the numbers: 412​=3=3x
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
3x=2π+8πn
3x=2π+8πn
3x=2π+8πn
Divide both sides by 3
3x=2π+8πn
Divide both sides by 333x​=32π​+38πn​
Simplifyx=32π​+38πn​
x=32π​+38πn​
Solve 43x​=23π​+2πn:x=2π+38πn​
43x​=23π​+2πn
Multiply both sides by 4
43x​=23π​+2πn
Multiply both sides by 444⋅3x​=4⋅23π​+4⋅2πn
Simplify
44⋅3x​=4⋅23π​+4⋅2πn
Simplify 44⋅3x​:3x
44⋅3x​
Multiply the numbers: 4⋅3=12=412x​
Divide the numbers: 412​=3=3x
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
3x=6π+8πn
3x=6π+8πn
3x=6π+8πn
Divide both sides by 3
3x=6π+8πn
Divide both sides by 333x​=36π​+38πn​
Simplifyx=2π+38πn​
x=2π+38πn​
x=32π​+38πn​,x=2π+38πn​
sin(4x​)=0:x=8πn,x=4π+8πn
sin(4x​)=0
General solutions for sin(4x​)=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​​​
4x​=0+2πn,4x​=π+2πn
4x​=0+2πn,4x​=π+2πn
Solve 4x​=0+2πn:x=8πn
4x​=0+2πn
0+2πn=2πn4x​=2πn
Multiply both sides by 4
4x​=2πn
Multiply both sides by 444x​=4⋅2πn
Simplifyx=8πn
x=8πn
Solve 4x​=π+2πn:x=4π+8πn
4x​=π+2πn
Multiply both sides by 4
4x​=π+2πn
Multiply both sides by 444x​=4π+4⋅2πn
Simplifyx=4π+8πn
x=4π+8πn
x=8πn,x=4π+8πn
Combine all the solutionsx=32π​+38πn​,x=2π+38πn​,x=8πn,x=4π+8πn
Combine all the solutionsx=2π+8πn,x=6π+8πn,x=38πn​,x=34π​+38πn​,x=32π​+38πn​,x=2π+38πn​,x=8πn,x=4π+8πn
Merge Overlapping Intervalsx=38πn​,x=34π​+38πn​,x=32π​+38πn​,x=2π+38πn​

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