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Popular Trigonometry >

2cos(x)+3tan(x)=3sec(x)

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Solution

2cos(x)+3tan(x)=3sec(x)

Solution

x=6π​+2πn,x=65π​+2πn
+1
Degrees
x=30∘+360∘n,x=150∘+360∘n
Solution steps
2cos(x)+3tan(x)=3sec(x)
Subtract 3sec(x) from both sides2cos(x)+3tan(x)−3sec(x)=0
Express with sin, cos2cos(x)+3⋅cos(x)sin(x)​−3⋅cos(x)1​=0
Simplify 2cos(x)+3⋅cos(x)sin(x)​−3⋅cos(x)1​:cos(x)2cos2(x)+3sin(x)−3​
2cos(x)+3⋅cos(x)sin(x)​−3⋅cos(x)1​
3⋅cos(x)sin(x)​=cos(x)3sin(x)​
3⋅cos(x)sin(x)​
Multiply fractions: a⋅cb​=ca⋅b​=cos(x)sin(x)⋅3​
3⋅cos(x)1​=cos(x)3​
3⋅cos(x)1​
Multiply fractions: a⋅cb​=ca⋅b​=cos(x)1⋅3​
Multiply the numbers: 1⋅3=3=cos(x)3​
=2cos(x)+cos(x)3sin(x)​−cos(x)3​
Combine the fractions cos(x)3sin(x)​−cos(x)3​:cos(x)3sin(x)−3​
Apply rule ca​±cb​=ca±b​=cos(x)3sin(x)−3​
=2cos(x)+cos(x)3sin(x)−3​
Convert element to fraction: 2cos(x)=cos(x)2cos(x)cos(x)​=cos(x)2cos(x)cos(x)​+cos(x)sin(x)⋅3−3​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=cos(x)2cos(x)cos(x)+sin(x)⋅3−3​
2cos(x)cos(x)+sin(x)⋅3−3=2cos2(x)+3sin(x)−3
2cos(x)cos(x)+sin(x)⋅3−3
2cos(x)cos(x)=2cos2(x)
2cos(x)cos(x)
Apply exponent rule: ab⋅ac=ab+ccos(x)cos(x)=cos1+1(x)=2cos1+1(x)
Add the numbers: 1+1=2=2cos2(x)
=2cos2(x)+3sin(x)−3
=cos(x)2cos2(x)+3sin(x)−3​
cos(x)2cos2(x)+3sin(x)−3​=0
g(x)f(x)​=0⇒f(x)=02cos2(x)+3sin(x)−3=0
Subtract 3sin(x) from both sides2cos2(x)−3=−3sin(x)
Square both sides(2cos2(x)−3)2=(−3sin(x))2
Subtract (−3sin(x))2 from both sides(2cos2(x)−3)2−9sin2(x)=0
Factor (2cos2(x)−3)2−9sin2(x):(2cos2(x)−3+3sin(x))(2cos2(x)−3−3sin(x))
(2cos2(x)−3)2−9sin2(x)
Rewrite (2cos2(x)−3)2−9sin2(x) as (2cos2(x)−3)2−(3sin(x))2
(2cos2(x)−3)2−9sin2(x)
Rewrite 9 as 32=(2cos2(x)−3)2−32sin2(x)
Apply exponent rule: ambm=(ab)m32sin2(x)=(3sin(x))2=(2cos2(x)−3)2−(3sin(x))2
=(2cos2(x)−3)2−(3sin(x))2
Apply Difference of Two Squares Formula: x2−y2=(x+y)(x−y)(2cos2(x)−3)2−(3sin(x))2=((2cos2(x)−3)+3sin(x))((2cos2(x)−3)−3sin(x))=((2cos2(x)−3)+3sin(x))((2cos2(x)−3)−3sin(x))
Refine=(2cos2(x)+3sin(x)−3)(2cos2(x)−3sin(x)−3)
(2cos2(x)−3+3sin(x))(2cos2(x)−3−3sin(x))=0
Solving each part separately2cos2(x)−3+3sin(x)=0or2cos2(x)−3−3sin(x)=0
2cos2(x)−3+3sin(x)=0:x=6π​+2πn,x=65π​+2πn,x=2π​+2πn
2cos2(x)−3+3sin(x)=0
Rewrite using trig identities
−3+2cos2(x)+3sin(x)
Use the Pythagorean identity: cos2(x)+sin2(x)=1cos2(x)=1−sin2(x)=−3+2(1−sin2(x))+3sin(x)
Simplify −3+2(1−sin2(x))+3sin(x):3sin(x)−2sin2(x)−1
−3+2(1−sin2(x))+3sin(x)
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⋅1−2sin2(x)
Multiply the numbers: 2⋅1=2=2−2sin2(x)
=−3+2−2sin2(x)+3sin(x)
Add/Subtract the numbers: −3+2=−1=3sin(x)−2sin2(x)−1
=3sin(x)−2sin2(x)−1
−1−2sin2(x)+3sin(x)=0
Solve by substitution
−1−2sin2(x)+3sin(x)=0
Let: sin(x)=u−1−2u2+3u=0
−1−2u2+3u=0:u=21​,u=1
−1−2u2+3u=0
Write in the standard form ax2+bx+c=0−2u2+3u−1=0
Solve with the quadratic formula
−2u2+3u−1=0
Quadratic Equation Formula:
For a=−2,b=3,c=−1u1,2​=2(−2)−3±32−4(−2)(−1)​​
u1,2​=2(−2)−3±32−4(−2)(−1)​​
32−4(−2)(−1)​=1
32−4(−2)(−1)​
Apply rule −(−a)=a=32−4⋅2⋅1​
Multiply the numbers: 4⋅2⋅1=8=32−8​
32=9=9−8​
Subtract the numbers: 9−8=1=1​
Apply rule 1​=1=1
u1,2​=2(−2)−3±1​
Separate the solutionsu1​=2(−2)−3+1​,u2​=2(−2)−3−1​
u=2(−2)−3+1​:21​
2(−2)−3+1​
Remove parentheses: (−a)=−a=−2⋅2−3+1​
Add/Subtract the numbers: −3+1=−2=−2⋅2−2​
Multiply the numbers: 2⋅2=4=−4−2​
Apply the fraction rule: −b−a​=ba​=42​
Cancel the common factor: 2=21​
u=2(−2)−3−1​:1
2(−2)−3−1​
Remove parentheses: (−a)=−a=−2⋅2−3−1​
Subtract the numbers: −3−1=−4=−2⋅2−4​
Multiply the numbers: 2⋅2=4=−4−4​
Apply the fraction rule: −b−a​=ba​=44​
Apply rule aa​=1=1
The solutions to the quadratic equation are:u=21​,u=1
Substitute back u=sin(x)sin(x)=21​,sin(x)=1
sin(x)=21​,sin(x)=1
sin(x)=21​:x=6π​+2πn,x=65π​+2πn
sin(x)=21​
General solutions for sin(x)=21​
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​​​
x=6π​+2πn,x=65π​+2πn
x=6π​+2πn,x=65π​+2πn
sin(x)=1:x=2π​+2πn
sin(x)=1
General solutions for sin(x)=1
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​​​
x=2π​+2πn
x=2π​+2πn
Combine all the solutionsx=6π​+2πn,x=65π​+2πn,x=2π​+2πn
2cos2(x)−3−3sin(x)=0:x=23π​+2πn,x=67π​+2πn,x=611π​+2πn
2cos2(x)−3−3sin(x)=0
Rewrite using trig identities
−3+2cos2(x)−3sin(x)
Use the Pythagorean identity: cos2(x)+sin2(x)=1cos2(x)=1−sin2(x)=−3+2(1−sin2(x))−3sin(x)
Simplify −3+2(1−sin2(x))−3sin(x):−2sin2(x)−3sin(x)−1
−3+2(1−sin2(x))−3sin(x)
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⋅1−2sin2(x)
Multiply the numbers: 2⋅1=2=2−2sin2(x)
=−3+2−2sin2(x)−3sin(x)
Add/Subtract the numbers: −3+2=−1=−2sin2(x)−3sin(x)−1
=−2sin2(x)−3sin(x)−1
−1−2sin2(x)−3sin(x)=0
Solve by substitution
−1−2sin2(x)−3sin(x)=0
Let: sin(x)=u−1−2u2−3u=0
−1−2u2−3u=0:u=−1,u=−21​
−1−2u2−3u=0
Write in the standard form ax2+bx+c=0−2u2−3u−1=0
Solve with the quadratic formula
−2u2−3u−1=0
Quadratic Equation Formula:
For a=−2,b=−3,c=−1u1,2​=2(−2)−(−3)±(−3)2−4(−2)(−1)​​
u1,2​=2(−2)−(−3)±(−3)2−4(−2)(−1)​​
(−3)2−4(−2)(−1)​=1
(−3)2−4(−2)(−1)​
Apply rule −(−a)=a=(−3)2−4⋅2⋅1​
Apply exponent rule: (−a)n=an,if n is even(−3)2=32=32−4⋅2⋅1​
Multiply the numbers: 4⋅2⋅1=8=32−8​
32=9=9−8​
Subtract the numbers: 9−8=1=1​
Apply rule 1​=1=1
u1,2​=2(−2)−(−3)±1​
Separate the solutionsu1​=2(−2)−(−3)+1​,u2​=2(−2)−(−3)−1​
u=2(−2)−(−3)+1​:−1
2(−2)−(−3)+1​
Remove parentheses: (−a)=−a,−(−a)=a=−2⋅23+1​
Add the numbers: 3+1=4=−2⋅24​
Multiply the numbers: 2⋅2=4=−44​
Apply the fraction rule: −ba​=−ba​=−44​
Apply rule aa​=1=−1
u=2(−2)−(−3)−1​:−21​
2(−2)−(−3)−1​
Remove parentheses: (−a)=−a,−(−a)=a=−2⋅23−1​
Subtract the numbers: 3−1=2=−2⋅22​
Multiply the numbers: 2⋅2=4=−42​
Apply the fraction rule: −ba​=−ba​=−42​
Cancel the common factor: 2=−21​
The solutions to the quadratic equation are:u=−1,u=−21​
Substitute back u=sin(x)sin(x)=−1,sin(x)=−21​
sin(x)=−1,sin(x)=−21​
sin(x)=−1:x=23π​+2πn
sin(x)=−1
General solutions for sin(x)=−1
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​​​
x=23π​+2πn
x=23π​+2πn
sin(x)=−21​:x=67π​+2πn,x=611π​+2πn
sin(x)=−21​
General solutions for sin(x)=−21​
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​​​
x=67π​+2πn,x=611π​+2πn
x=67π​+2πn,x=611π​+2πn
Combine all the solutionsx=23π​+2πn,x=67π​+2πn,x=611π​+2πn
Combine all the solutionsx=6π​+2πn,x=65π​+2πn,x=2π​+2πn,x=23π​+2πn,x=67π​+2πn,x=611π​+2πn
Verify solutions by plugging them into the original equation
Check the solutions by plugging them into 2cos(x)+3tan(x)=3sec(x)
Remove the ones that don't agree with the equation.
Check the solution 6π​+2πn:True
6π​+2πn
Plug in n=16π​+2π1
For 2cos(x)+3tan(x)=3sec(x)plug inx=6π​+2π12cos(6π​+2π1)+3tan(6π​+2π1)=3sec(6π​+2π1)
Refine3.46410…=3.46410…
⇒True
Check the solution 65π​+2πn:True
65π​+2πn
Plug in n=165π​+2π1
For 2cos(x)+3tan(x)=3sec(x)plug inx=65π​+2π12cos(65π​+2π1)+3tan(65π​+2π1)=3sec(65π​+2π1)
Refine−3.46410…=−3.46410…
⇒True
Check the solution 2π​+2πn:True
2π​+2πn
Plug in n=12π​+2π1
For 2cos(x)+3tan(x)=3sec(x)plug inx=2π​+2π12cos(2π​+2π1)+3tan(2π​+2π1)=3sec(2π​+2π1)
Refine∞=∞
⇒True
Check the solution 23π​+2πn:False
23π​+2πn
Plug in n=123π​+2π1
For 2cos(x)+3tan(x)=3sec(x)plug inx=23π​+2π12cos(23π​+2π1)+3tan(23π​+2π1)=3sec(23π​+2π1)
Refine∞=−∞
⇒False
Check the solution 67π​+2πn:False
67π​+2πn
Plug in n=167π​+2π1
For 2cos(x)+3tan(x)=3sec(x)plug inx=67π​+2π12cos(67π​+2π1)+3tan(67π​+2π1)=3sec(67π​+2π1)
Refine0=−3.46410…
⇒False
Check the solution 611π​+2πn:False
611π​+2πn
Plug in n=1611π​+2π1
For 2cos(x)+3tan(x)=3sec(x)plug inx=611π​+2π12cos(611π​+2π1)+3tan(611π​+2π1)=3sec(611π​+2π1)
Refine0=3.46410…
⇒False
x=6π​+2πn,x=65π​+2πn,x=2π​+2πn
Since the equation is undefined for:2π​+2πnx=6π​+2πn,x=65π​+2πn

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Frequently Asked Questions (FAQ)

  • What is the general solution for 2cos(x)+3tan(x)=3sec(x) ?

    The general solution for 2cos(x)+3tan(x)=3sec(x) is x= pi/6+2pin,x=(5pi)/6+2pin
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