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Popular Trigonometry >

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

  • Pre Algebra
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Solution

sin2(x)=cos2(2x​)

Solution

x=−3π​−38πn​,x=−35π​−38πn​,x=38πn​+3π​,x=35π​+38πn​
+1
Degrees
x=−60∘−480∘n,x=−300∘−480∘n,x=60∘+480∘n,x=300∘+480∘n
Solution steps
sin2(x)=cos2(2x​)
Subtract cos2(2x​) from both sidessin2(x)−cos2(2x​)=0
Rewrite using trig identities
−cos2(2x​)+sin2(x)
Use the following identity: cos(x)=sin(2π​−x)=−sin2(2π​−2x​)+sin2(x)
Apply rule ca​±cb​=ca±b​=−sin2(2π−x​)+sin2(x)
−sin2(2−x+π​)+sin2(x)=0
Factor −sin2(2−x+π​)+sin2(x):(sin(x)+sin(2−x+π​))(sin(x)−sin(2−x+π​))
−sin2(2−x+π​)+sin2(x)
Apply Difference of Two Squares Formula: x2−y2=(x+y)(x−y)sin2(x)−sin2(2−x+π​)=(sin(x)+sin(2−x+π​))(sin(x)−sin(2−x+π​))=(sin(x)+sin(2−x+π​))(sin(x)−sin(2−x+π​))
(sin(x)+sin(2−x+π​))(sin(x)−sin(2−x+π​))=0
Solving each part separatelysin(x)+sin(2−x+π​)=0orsin(x)−sin(2−x+π​)=0
sin(x)+sin(2−x+π​)=0:x=−3π​−38πn​,x=−35π​−38πn​,x=8πn−π,x=3π+8πn
sin(x)+sin(2−x+π​)=0
Rewrite using trig identities
sin(2−x+π​)+sin(x)
Use the Sum to Product identity: sin(s)+sin(t)=2sin(2s+t​)cos(2s−t​)=2sin(22−x+π​+x​)cos(22−x+π​−x​)
Simplify 2sin(22−x+π​+x​)cos(22−x+π​−x​):2sin(4x+π​)cos(4−3x+π​)
2sin(22−x+π​+x​)cos(22−x+π​−x​)
22−x+π​+x​=4x+π​
22−x+π​+x​
Join 2−x+π​+x:2x+π​
2−x+π​+x
Convert element to fraction: x=2x2​=2−x+π​+2x⋅2​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2−x+π+x⋅2​
−x+π+x⋅2=x+π
−x+π+x⋅2
Group like terms=−x+2x+π
Add similar elements: −x+2x=x=x+π
=2x+π​
=22x+π​​
Apply the fraction rule: acb​​=c⋅ab​=2⋅2x+π​
Multiply the numbers: 2⋅2=4=4x+π​
=2sin(4x+π​)cos(22−x+π​−x​)
22−x+π​−x​=4−3x+π​
22−x+π​−x​
Join 2−x+π​−x:2−3x+π​
2−x+π​−x
Convert element to fraction: x=2x2​=2−x+π​−2x⋅2​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2−x+π−x⋅2​
−x+π−x⋅2=−3x+π
−x+π−x⋅2
Group like terms=−x−2x+π
Add similar elements: −x−2x=−3x=−3x+π
=2−3x+π​
=22−3x+π​​
Apply the fraction rule: acb​​=c⋅ab​=2⋅2−3x+π​
Multiply the numbers: 2⋅2=4=4−3x+π​
=2sin(4x+π​)cos(4−3x+π​)
=2sin(4x+π​)cos(4−3x+π​)
2cos(4π−3x​)sin(4x+π​)=0
Solving each part separatelycos(4π−3x​)=0orsin(4x+π​)=0
cos(4π−3x​)=0:x=−3π​−38πn​,x=−35π​−38πn​
cos(4π−3x​)=0
General solutions for cos(4π−3x​)=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​​​​
4π−3x​=2π​+2πn,4π−3x​=23π​+2πn
4π−3x​=2π​+2πn,4π−3x​=23π​+2πn
Solve 4π−3x​=2π​+2πn:x=−3π​−38πn​
4π−3x​=2π​+2πn
Multiply both sides by 4
4π−3x​=2π​+2πn
Multiply both sides by 444(π−3x)​=4⋅2π​+4⋅2πn
Simplify
44(π−3x)​=4⋅2π​+4⋅2πn
Simplify 44(π−3x)​:π−3x
44(π−3x)​
Divide the numbers: 44​=1=π−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
π−3x=2π+8πn
π−3x=2π+8πn
π−3x=2π+8πn
Move πto the right side
π−3x=2π+8πn
Subtract π from both sidesπ−3x−π=2π+8πn−π
Simplify−3x=π+8πn
−3x=π+8πn
Divide both sides by −3
−3x=π+8πn
Divide both sides by −3−3−3x​=−3π​+−38πn​
Simplify
−3−3x​=−3π​+−38πn​
Simplify −3−3x​:x
−3−3x​
Apply the fraction rule: −b−a​=ba​=33x​
Divide the numbers: 33​=1=x
Simplify −3π​+−38πn​:−3π​−38πn​
−3π​+−38πn​
Apply the fraction rule: −ba​=−ba​=−3π​+−38πn​
Apply the fraction rule: −ba​=−ba​=−3π​−38πn​
x=−3π​−38πn​
x=−3π​−38πn​
x=−3π​−38πn​
Solve 4π−3x​=23π​+2πn:x=−35π​−38πn​
4π−3x​=23π​+2πn
Multiply both sides by 4
4π−3x​=23π​+2πn
Multiply both sides by 444(π−3x)​=4⋅23π​+4⋅2πn
Simplify
44(π−3x)​=4⋅23π​+4⋅2πn
Simplify 44(π−3x)​:π−3x
44(π−3x)​
Divide the numbers: 44​=1=π−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
π−3x=6π+8πn
π−3x=6π+8πn
π−3x=6π+8πn
Move πto the right side
π−3x=6π+8πn
Subtract π from both sidesπ−3x−π=6π+8πn−π
Simplify−3x=5π+8πn
−3x=5π+8πn
Divide both sides by −3
−3x=5π+8πn
Divide both sides by −3−3−3x​=−35π​+−38πn​
Simplify
−3−3x​=−35π​+−38πn​
Simplify −3−3x​:x
−3−3x​
Apply the fraction rule: −b−a​=ba​=33x​
Divide the numbers: 33​=1=x
Simplify −35π​+−38πn​:−35π​−38πn​
−35π​+−38πn​
Apply the fraction rule: −ba​=−ba​=−35π​+−38πn​
Apply the fraction rule: −ba​=−ba​=−35π​−38πn​
x=−35π​−38πn​
x=−35π​−38πn​
x=−35π​−38πn​
x=−3π​−38πn​,x=−35π​−38πn​
sin(4x+π​)=0:x=8πn−π,x=3π+8πn
sin(4x+π​)=0
General solutions for sin(4x+π​)=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+π​=0+2πn,4x+π​=π+2πn
4x+π​=0+2πn,4x+π​=π+2πn
Solve 4x+π​=0+2πn:x=8πn−π
4x+π​=0+2πn
0+2πn=2πn4x+π​=2πn
Multiply both sides by 4
4x+π​=2πn
Multiply both sides by 444(x+π)​=4⋅2πn
Simplifyx+π=8πn
x+π=8πn
Move πto the right side
x+π=8πn
Subtract π from both sidesx+π−π=8πn−π
Simplifyx=8πn−π
x=8πn−π
Solve 4x+π​=π+2πn:x=3π+8πn
4x+π​=π+2πn
Multiply both sides by 4
4x+π​=π+2πn
Multiply both sides by 444(x+π)​=4π+4⋅2πn
Simplifyx+π=4π+8πn
x+π=4π+8πn
Move πto the right side
x+π=4π+8πn
Subtract π from both sidesx+π−π=4π+8πn−π
Simplifyx=3π+8πn
x=3π+8πn
x=8πn−π,x=3π+8πn
Combine all the solutionsx=−3π​−38πn​,x=−35π​−38πn​,x=8πn−π,x=3π+8πn
sin(x)−sin(2−x+π​)=0:x=π+8πn,x=5π+8πn,x=38πn​+3π​,x=35π​+38πn​
sin(x)−sin(2−x+π​)=0
Rewrite using trig identities
−sin(2−x+π​)+sin(x)
Use the Sum to Product identity: sin(s)−sin(t)=2sin(2s−t​)cos(2s+t​)=2sin(2x−2−x+π​​)cos(2x+2−x+π​​)
Simplify 2sin(2x−2−x+π​​)cos(2x+2−x+π​​):2sin(43x−π​)cos(4x+π​)
2sin(2x−2−x+π​​)cos(2x+2−x+π​​)
2x−2−x+π​​=43x−π​
2x−2−x+π​​
Join x−2−x+π​:23x−π​
x−2−x+π​
Convert element to fraction: x=2x2​=2x⋅2​−2−x+π​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2x⋅2−(−x+π)​
Expand x⋅2−(−x+π):3x−π
x⋅2−(−x+π)
=2x−(−x+π)
−(−x+π):x−π
−(−x+π)
Distribute parentheses=−(−x)−(π)
Apply minus-plus rules−(−a)=a,−(a)=−a=x−π
=x⋅2+x−π
Add similar elements: 2x+x=3x=3x−π
=23x−π​
=223x−π​​
Apply the fraction rule: acb​​=c⋅ab​=2⋅23x−π​
Multiply the numbers: 2⋅2=4=43x−π​
=2sin(43x−π​)cos(2x+2−x+π​​)
2x+2−x+π​​=4x+π​
2x+2−x+π​​
Join x+2−x+π​:2x+π​
x+2−x+π​
Convert element to fraction: x=2x2​=2x⋅2​+2−x+π​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=2x⋅2−x+π​
Add similar elements: 2x−x=x=2x+π​
=22x+π​​
Apply the fraction rule: acb​​=c⋅ab​=2⋅2x+π​
Multiply the numbers: 2⋅2=4=4x+π​
=2sin(43x−π​)cos(4x+π​)
=2sin(43x−π​)cos(4x+π​)
2cos(4x+π​)sin(4−π+3x​)=0
Solving each part separatelycos(4x+π​)=0orsin(4−π+3x​)=0
cos(4x+π​)=0:x=π+8πn,x=5π+8πn
cos(4x+π​)=0
General solutions for cos(4x+π​)=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+π​=2π​+2πn,4x+π​=23π​+2πn
4x+π​=2π​+2πn,4x+π​=23π​+2πn
Solve 4x+π​=2π​+2πn:x=π+8πn
4x+π​=2π​+2πn
Multiply both sides by 4
4x+π​=2π​+2πn
Multiply both sides by 444(x+π)​=4⋅2π​+4⋅2πn
Simplify
44(x+π)​=4⋅2π​+4⋅2πn
Simplify 44(x+π)​:x+π
44(x+π)​
Divide the numbers: 44​=1=x+π
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+π=2π+8πn
x+π=2π+8πn
x+π=2π+8πn
Move πto the right side
x+π=2π+8πn
Subtract π from both sidesx+π−π=2π+8πn−π
Simplifyx=π+8πn
x=π+8πn
Solve 4x+π​=23π​+2πn:x=5π+8πn
4x+π​=23π​+2πn
Multiply both sides by 4
4x+π​=23π​+2πn
Multiply both sides by 444(x+π)​=4⋅23π​+4⋅2πn
Simplify
44(x+π)​=4⋅23π​+4⋅2πn
Simplify 44(x+π)​:x+π
44(x+π)​
Divide the numbers: 44​=1=x+π
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+π=6π+8πn
x+π=6π+8πn
x+π=6π+8πn
Move πto the right side
x+π=6π+8πn
Subtract π from both sidesx+π−π=6π+8πn−π
Simplifyx=5π+8πn
x=5π+8πn
x=π+8πn,x=5π+8πn
sin(4−π+3x​)=0:x=38πn​+3π​,x=35π​+38πn​
sin(4−π+3x​)=0
General solutions for sin(4−π+3x​)=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​​​
4−π+3x​=0+2πn,4−π+3x​=π+2πn
4−π+3x​=0+2πn,4−π+3x​=π+2πn
Solve 4−π+3x​=0+2πn:x=38πn​+3π​
4−π+3x​=0+2πn
0+2πn=2πn4−π+3x​=2πn
Multiply both sides by 4
4−π+3x​=2πn
Multiply both sides by 444(−π+3x)​=4⋅2πn
Simplify−π+3x=8πn
−π+3x=8πn
Move πto the right side
−π+3x=8πn
Add π to both sides−π+3x+π=8πn+π
Simplify3x=8πn+π
3x=8πn+π
Divide both sides by 3
3x=8πn+π
Divide both sides by 333x​=38πn​+3π​
Simplifyx=38πn​+3π​
x=38πn​+3π​
Solve 4−π+3x​=π+2πn:x=35π​+38πn​
4−π+3x​=π+2πn
Multiply both sides by 4
4−π+3x​=π+2πn
Multiply both sides by 444(−π+3x)​=4π+4⋅2πn
Simplify−π+3x=4π+8πn
−π+3x=4π+8πn
Move πto the right side
−π+3x=4π+8πn
Add π to both sides−π+3x+π=4π+8πn+π
Simplify3x=5π+8πn
3x=5π+8πn
Divide both sides by 3
3x=5π+8πn
Divide both sides by 333x​=35π​+38πn​
Simplifyx=35π​+38πn​
x=35π​+38πn​
x=38πn​+3π​,x=35π​+38πn​
Combine all the solutionsx=π+8πn,x=5π+8πn,x=38πn​+3π​,x=35π​+38πn​
Combine all the solutionsx=−3π​−38πn​,x=−35π​−38πn​,x=8πn−π,x=3π+8πn,x=π+8πn,x=5π+8πn,x=38πn​+3π​,x=35π​+38πn​
Merge Overlapping Intervalsx=−3π​−38πn​,x=−35π​−38πn​,x=38πn​+3π​,x=35π​+38πn​

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