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Popular Trigonometry >

cos^3(3θ)= 1/4

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Solution

cos3(3θ)=41​

Solution

θ=30.88929…​+32πn​,θ=32π​−30.88929…​+32πn​
+1
Degrees
θ=16.98426…∘+120∘n,θ=103.01573…∘+120∘n
Solution steps
cos3(3θ)=41​
Solve by substitution
cos3(3θ)=41​
Let: cos(3θ)=uu3=41​
u3=41​
For x3=f(a) the solutions are
Simplify
Multiply fractions: a⋅cb​=ca⋅b​
Apply radical rule: assuming a≥0,b≥0
Apply rule
Multiply
Multiply fractions: a⋅cb​=ca⋅b​
1⋅(−1+3​i)=−1+3​i
1⋅(−1+3​i)
Multiply: 1⋅(−1+3​i)=(−1+3​i)=(−1+3​i)
Remove parentheses: (−a)=−a=−1+3​i
Apply the fraction rule: acb​​=c⋅ab​
Rationalize
Multiply by the conjugate 432​432​​
Apply exponent rule: ab⋅ac=ab+c=432​+31​⋅2
432​+31​=4
432​+31​
Combine the fractions 32​+31​:1
Apply rule ca​±cb​=ca±b​=32+1​
Add the numbers: 2+1=3=33​
Apply rule aa​=1=1
=41
Apply rule a1=a=4
=4⋅2
Multiply the numbers: 4⋅2=8=8
=8432​(−1+3​i)​
=8432​(−1+3​i)​
Rewrite 8432​(−1+3​i)​ in standard complex form: −8432​​+8432​3​​i
8432​(−1+3​i)​
Expand 432​(−1+3​i):−432​+432​3​i
432​(−1+3​i)
Apply the distributive law: a(b+c)=ab+aca=432​,b=−1,c=3​i=432​(−1)+432​3​i
Apply minus-plus rules+(−a)=−a=−1⋅432​+432​3​i
Multiply: 1⋅432​=432​=−432​+432​3​i
=8−432​+432​3​i​
Apply the fraction rule: ca±b​=ca​±cb​8−432​+432​3​i​=−8432​​+8432​3​i​=−8432​​+8432​3​i​
=−8432​​+8432​3​​i
Simplify
Multiply fractions: a⋅cb​=ca⋅b​
Apply radical rule: assuming a≥0,b≥0
Apply rule
Multiply
Multiply fractions: a⋅cb​=ca⋅b​
1⋅(−1−3​i)=−1−3​i
1⋅(−1−3​i)
Multiply: 1⋅(−1−3​i)=(−1−3​i)=(−1−3​i)
Remove parentheses: (−a)=−a=−1−3​i
Apply the fraction rule: acb​​=c⋅ab​
Rationalize
Multiply by the conjugate 432​432​​
Apply exponent rule: ab⋅ac=ab+c=432​+31​⋅2
432​+31​=4
432​+31​
Combine the fractions 32​+31​:1
Apply rule ca​±cb​=ca±b​=32+1​
Add the numbers: 2+1=3=33​
Apply rule aa​=1=1
=41
Apply rule a1=a=4
=4⋅2
Multiply the numbers: 4⋅2=8=8
=8432​(−1−3​i)​
=8432​(−1−3​i)​
Rewrite 8432​(−1−3​i)​ in standard complex form: −8432​​−8432​3​​i
8432​(−1−3​i)​
Expand 432​(−1−3​i):−432​−432​3​i
432​(−1−3​i)
Apply the distributive law: a(b−c)=ab−aca=432​,b=−1,c=3​i=432​(−1)−432​3​i
Apply minus-plus rules+(−a)=−a=−1⋅432​−432​3​i
Multiply: 1⋅432​=432​=−432​−432​3​i
=8−432​−432​3​i​
Apply the fraction rule: ca±b​=ca​±cb​8−432​−432​3​i​=−8432​​−8432​3​i​=−8432​​−8432​3​i​
=−8432​​−8432​3​​i
Substitute back u=cos(3θ)
Apply trig inverse properties
General solutions for cos(x)=a⇒x=arccos(a)+2πn,x=2π−arccos(a)+2πn
Solve
Divide both sides by 3
Divide both sides by 3
Simplify
Solve
Divide both sides by 3
Divide both sides by 3
Simplify
cos(3θ)=−8432​​+i8432​3​​:No Solution
cos(3θ)=−8432​​+i8432​3​​
Simplify
−8432​​+i8432​3​​
Cancel
8432​​
Factor 432​:234​
Factor 4=22=(22)32​
Simplify (22)32​:234​
(22)32​
Apply exponent rule: (ab)c=abc, assuming a≥0=22⋅32​
2⋅32​=34​
2⋅32​
Multiply fractions: a⋅cb​=ca⋅b​=32⋅2​
Multiply the numbers: 2⋅2=4=34​
=234​
=234​
Factor 8:23
Factor 8=23
=23234​​
Cancel
23234​​
234​=21+31​,23=21+2=21+221+31​​
Apply exponent rule: ab+c=abac21+31​=21⋅231​,21+2=21⋅22=22⋅2121⋅231​​
Cancel the common factor: 21=22231​​
=20+220+31​​
Apply exponent rule: ab+c=abac20+31​=20⋅231​,20+2=20⋅22=22⋅2020⋅231​​
Cancel the common factor: 20=22231​​
22=4
Cancel
Factor 4:22
Factor 4=22
Cancel
=20+220+31​​
Apply exponent rule: ab+c=abac20+31​=20⋅231​,20+2=20⋅22=22⋅2020⋅231​​
Cancel the common factor: 20=22231​​
=20+220+31​​
Apply exponent rule: ab+c=abac20+31​=20⋅231​,20+2=20⋅22=22⋅2020⋅231​​
Cancel the common factor: 20=22231​​
Rewrite in standard complex form:
Apply radical rule: =22231​​
Apply exponent rule: xbxa​=xb−a1​22231​​=22−31​1​=22−31​1​
Subtract the numbers: 2−31​=35​=235​1​
235​=2⋅232​
235​
235​=21+32​=21+32​
Apply exponent rule: xa+b=xaxb=21⋅232​
Refine=2⋅232​
=2⋅232​1​
i8432​3​​=8432​3​i​
i8432​3​​
Multiply fractions: a⋅cb​=ca⋅b​=8432​3​i​
=−2⋅232​1​+8432​3​i​
Least Common Multiplier of 2232​,8:8⋅232​
2⋅232​,8
Lowest Common Multiplier (LCM)
Least Common Multiplier of 2,8:8
2,8
Least Common Multiplier (LCM)
Prime factorization of 2:2
2
2 is a prime number, therefore no factorization is possible=2
Prime factorization of 8:2⋅2⋅2
8
8divides by 28=4⋅2=2⋅4
4divides by 24=2⋅2=2⋅2⋅2
Multiply each factor the greatest number of times it occurs in either 2 or 8=2⋅2⋅2
Multiply the numbers: 2⋅2⋅2=8=8
Compute an expression comprised of factors that appear either in 2232​ or 8=8⋅232​
Adjust Fractions based on the LCM
Multiply each numerator by the same amount needed to multiply its
corresponding denominator to turn it into the LCM 8⋅232​
For 2⋅232​1​:multiply the denominator and numerator by 42⋅232​1​=2⋅232​⋅41⋅4​=8⋅232​4​
For 8432​3​i​:multiply the denominator and numerator by 232​8432​3​i​=8⋅232​432​3​i232​​=8⋅232​3​⋅234​+32​i​
=−8⋅232​4​+8⋅232​3​⋅234​+32​i​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=8⋅232​−4+3​⋅234​+32​i​
3​⋅234​+32​i=43​i
3​⋅234​+32​i
234​+32​=22
234​+32​
Join 34​+32​:2
34​+32​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=34+2​
Add the numbers: 4+2=6=36​
Divide the numbers: 36​=2=2
=22
=223​i
22=4=43​i
=8⋅232​−4+43​i​
Factor −4+3​4i:4(−1+3​i)
−4+3​⋅4i
Rewrite as=−4⋅1+43​i
Factor out common term 4=4(−1+3​i)
=8⋅232​4(−1+3​i)​
Cancel the common factor: 4=2⋅232​−1+3​i​
Apply the fraction rule: ca±b​=ca​±cb​2⋅232​−1+3​i​=−2⋅232​1​+2⋅232​3​i​=−2⋅232​1​+2⋅232​3​i​
2⋅232​3​​
Multiply by the conjugate
Apply exponent rule: ab⋅ac=ab+c=21+32​+31​
Join 1+32​+31​:2
1+32​+31​
Convert element to fraction: 1=11​=11​+32​+31​
Least Common Multiplier of 1,3,3:3
1,3,3
Least Common Multiplier (LCM)
Prime factorization of 1
Prime factorization of 3:3
3
3 is a prime number, therefore no factorization is possible=3
Prime factorization of 3:3
3
3 is a prime number, therefore no factorization is possible=3
Compute a number comprised of factors that appear in at least one of the following:
1,3,3
=3
Multiply the numbers: 3=3=3
Adjust Fractions based on the LCM
Multiply each numerator by the same amount needed to multiply its
corresponding denominator to turn it into the LCM 3
For 11​:multiply the denominator and numerator by 311​=1⋅31⋅3​=33​
=33​+32​+31​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=33+2+1​
Add the numbers: 3+2+1=6=36​
Divide the numbers: 36​=2=2
=22
22=4=4
−2⋅232​1​
Multiply by the conjugate
Apply exponent rule: ab⋅ac=ab+c=21+32​+31​
Join 1+32​+31​:2
1+32​+31​
Convert element to fraction: 1=11​=11​+32​+31​
Least Common Multiplier of 1,3,3:3
1,3,3
Least Common Multiplier (LCM)
Prime factorization of 1
Prime factorization of 3:3
3
3 is a prime number, therefore no factorization is possible=3
Prime factorization of 3:3
3
3 is a prime number, therefore no factorization is possible=3
Compute a number comprised of factors that appear in at least one of the following:
1,3,3
=3
Multiply the numbers: 3=3=3
Adjust Fractions based on the LCM
Multiply each numerator by the same amount needed to multiply its
corresponding denominator to turn it into the LCM 3
For 11​:multiply the denominator and numerator by 311​=1⋅31⋅3​=33​
=33​+32​+31​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=33+2+1​
Add the numbers: 3+2+1=6=36​
Divide the numbers: 36​=2=2
=22
22=4=4
NoSolution
cos(3θ)=−8432​​−i8432​3​​:No Solution
cos(3θ)=−8432​​−i8432​3​​
Simplify
−8432​​−i8432​3​​
Cancel
8432​​
Factor 432​:234​
Factor 4=22=(22)32​
Simplify (22)32​:234​
(22)32​
Apply exponent rule: (ab)c=abc, assuming a≥0=22⋅32​
2⋅32​=34​
2⋅32​
Multiply fractions: a⋅cb​=ca⋅b​=32⋅2​
Multiply the numbers: 2⋅2=4=34​
=234​
=234​
Factor 8:23
Factor 8=23
=23234​​
Cancel
23234​​
234​=21+31​,23=21+2=21+221+31​​
Apply exponent rule: ab+c=abac21+31​=21⋅231​,21+2=21⋅22=22⋅2121⋅231​​
Cancel the common factor: 21=22231​​
=20+220+31​​
Apply exponent rule: ab+c=abac20+31​=20⋅231​,20+2=20⋅22=22⋅2020⋅231​​
Cancel the common factor: 20=22231​​
22=4
Cancel
Factor 4:22
Factor 4=22
Cancel
=20+220+31​​
Apply exponent rule: ab+c=abac20+31​=20⋅231​,20+2=20⋅22=22⋅2020⋅231​​
Cancel the common factor: 20=22231​​
=20+220+31​​
Apply exponent rule: ab+c=abac20+31​=20⋅231​,20+2=20⋅22=22⋅2020⋅231​​
Cancel the common factor: 20=22231​​
Rewrite in standard complex form:
Apply radical rule: =22231​​
Apply exponent rule: xbxa​=xb−a1​22231​​=22−31​1​=22−31​1​
Subtract the numbers: 2−31​=35​=235​1​
235​=2⋅232​
235​
235​=21+32​=21+32​
Apply exponent rule: xa+b=xaxb=21⋅232​
Refine=2⋅232​
=2⋅232​1​
i8432​3​​=8432​3​i​
i8432​3​​
Multiply fractions: a⋅cb​=ca⋅b​=8432​3​i​
=−2⋅232​1​−8432​3​i​
Least Common Multiplier of 2232​,8:8⋅232​
2⋅232​,8
Lowest Common Multiplier (LCM)
Least Common Multiplier of 2,8:8
2,8
Least Common Multiplier (LCM)
Prime factorization of 2:2
2
2 is a prime number, therefore no factorization is possible=2
Prime factorization of 8:2⋅2⋅2
8
8divides by 28=4⋅2=2⋅4
4divides by 24=2⋅2=2⋅2⋅2
Multiply each factor the greatest number of times it occurs in either 2 or 8=2⋅2⋅2
Multiply the numbers: 2⋅2⋅2=8=8
Compute an expression comprised of factors that appear either in 2232​ or 8=8⋅232​
Adjust Fractions based on the LCM
Multiply each numerator by the same amount needed to multiply its
corresponding denominator to turn it into the LCM 8⋅232​
For 2⋅232​1​:multiply the denominator and numerator by 42⋅232​1​=2⋅232​⋅41⋅4​=8⋅232​4​
For 8432​3​i​:multiply the denominator and numerator by 232​8432​3​i​=8⋅232​432​3​i232​​=8⋅232​3​⋅234​+32​i​
=−8⋅232​4​−8⋅232​3​⋅234​+32​i​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=8⋅232​−4−3​⋅234​+32​i​
3​⋅234​+32​i=43​i
3​⋅234​+32​i
234​+32​=22
234​+32​
Join 34​+32​:2
34​+32​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=34+2​
Add the numbers: 4+2=6=36​
Divide the numbers: 36​=2=2
=22
=223​i
22=4=43​i
=8⋅232​−4−43​i​
Factor −4−3​4i:−4(1+3​i)
−4−3​⋅4i
Rewrite as=−4⋅1−43​i
Factor out common term 4=−4(1+3​i)
=−8⋅232​4(1+3​i)​
Cancel the common factor: 4=−2⋅232​1+3​i​
Apply the fraction rule: ca±b​=ca​±cb​2⋅232​1+3​i​=−(2⋅232​1​)−(2⋅232​3​i​)=−(2⋅232​1​)−(2⋅232​3​i​)
Remove parentheses: (a)=a=−2⋅232​1​−2⋅232​3​i​
−2⋅232​3​​
Multiply by the conjugate
Apply exponent rule: ab⋅ac=ab+c=21+32​+31​
Join 1+32​+31​:2
1+32​+31​
Convert element to fraction: 1=11​=11​+32​+31​
Least Common Multiplier of 1,3,3:3
1,3,3
Least Common Multiplier (LCM)
Prime factorization of 1
Prime factorization of 3:3
3
3 is a prime number, therefore no factorization is possible=3
Prime factorization of 3:3
3
3 is a prime number, therefore no factorization is possible=3
Compute a number comprised of factors that appear in at least one of the following:
1,3,3
=3
Multiply the numbers: 3=3=3
Adjust Fractions based on the LCM
Multiply each numerator by the same amount needed to multiply its
corresponding denominator to turn it into the LCM 3
For 11​:multiply the denominator and numerator by 311​=1⋅31⋅3​=33​
=33​+32​+31​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=33+2+1​
Add the numbers: 3+2+1=6=36​
Divide the numbers: 36​=2=2
=22
22=4=4
−2⋅232​1​
Multiply by the conjugate
Apply exponent rule: ab⋅ac=ab+c=21+32​+31​
Join 1+32​+31​:2
1+32​+31​
Convert element to fraction: 1=11​=11​+32​+31​
Least Common Multiplier of 1,3,3:3
1,3,3
Least Common Multiplier (LCM)
Prime factorization of 1
Prime factorization of 3:3
3
3 is a prime number, therefore no factorization is possible=3
Prime factorization of 3:3
3
3 is a prime number, therefore no factorization is possible=3
Compute a number comprised of factors that appear in at least one of the following:
1,3,3
=3
Multiply the numbers: 3=3=3
Adjust Fractions based on the LCM
Multiply each numerator by the same amount needed to multiply its
corresponding denominator to turn it into the LCM 3
For 11​:multiply the denominator and numerator by 311​=1⋅31⋅3​=33​
=33​+32​+31​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=33+2+1​
Add the numbers: 3+2+1=6=36​
Divide the numbers: 36​=2=2
=22
22=4=4
NoSolution
Combine all the solutions
Show solutions in decimal formθ=30.88929…​+32πn​,θ=32π​−30.88929…​+32πn​

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Popular Examples

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Frequently Asked Questions (FAQ)

  • What is the general solution for cos^3(3θ)= 1/4 ?

    The general solution for cos^3(3θ)= 1/4 is θ=(0.88929…)/3+(2pin)/3 ,θ=(2pi)/3-(0.88929…)/3+(2pin)/3
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