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Popular Trigonometry >

cos(pi/2-x)tan(x)-sec(-x)=1

  • Pre Algebra
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Solution

cos(2π​−x)tan(x)−sec(−x)=1

Solution

x=π+2πn
+1
Degrees
x=180∘+360∘n
Solution steps
cos(2π​−x)tan(x)−sec(−x)=1
Rewrite using trig identities
cos(2π​−x)tan(x)−sec(−x)=1
Rewrite using trig identities
cos(2π​−x)
Use the Angle Difference identity: cos(s−t)=cos(s)cos(t)+sin(s)sin(t)=cos(2π​)cos(x)+sin(2π​)sin(x)
Simplify cos(2π​)cos(x)+sin(2π​)sin(x):sin(x)
cos(2π​)cos(x)+sin(2π​)sin(x)
cos(2π​)cos(x)=0
cos(2π​)cos(x)
Simplify cos(2π​):0
cos(2π​)
Use the following trivial identity:cos(2π​)=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​​​​
=0
=0⋅cos(x)
Apply rule 0⋅a=0=0
sin(2π​)sin(x)=sin(x)
sin(2π​)sin(x)
Simplify sin(2π​):1
sin(2π​)
Use the following trivial identity:sin(2π​)=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​​​
=1
=1⋅sin(x)
Multiply: 1⋅sin(x)=sin(x)=sin(x)
=0+sin(x)
0+sin(x)=sin(x)=sin(x)
=sin(x)
−sec(x)+sin(x)tan(x)=1
−sec(x)+sin(x)tan(x)=1
Subtract 1 from both sides−sec(x)+sin(x)tan(x)−1=0
Express with sin, cos−cos(x)1​+sin(x)cos(x)sin(x)​−1=0
Simplify −cos(x)1​+sin(x)cos(x)sin(x)​−1:cos(x)−1+sin2(x)−cos(x)​
−cos(x)1​+sin(x)cos(x)sin(x)​−1
sin(x)cos(x)sin(x)​=cos(x)sin2(x)​
sin(x)cos(x)sin(x)​
Multiply fractions: a⋅cb​=ca⋅b​=cos(x)sin(x)sin(x)​
sin(x)sin(x)=sin2(x)
sin(x)sin(x)
Apply exponent rule: ab⋅ac=ab+csin(x)sin(x)=sin1+1(x)=sin1+1(x)
Add the numbers: 1+1=2=sin2(x)
=cos(x)sin2(x)​
=−cos(x)1​+cos(x)sin2(x)​−1
Combine the fractions −cos(x)1​+cos(x)sin2(x)​:cos(x)−1+sin2(x)​
Apply rule ca​±cb​=ca±b​=cos(x)−1+sin2(x)​
=cos(x)sin2(x)−1​−1
Convert element to fraction: 1=cos(x)1cos(x)​=cos(x)−1+sin2(x)​−cos(x)1⋅cos(x)​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=cos(x)−1+sin2(x)−1⋅cos(x)​
Multiply: 1⋅cos(x)=cos(x)=cos(x)−1+sin2(x)−cos(x)​
cos(x)−1+sin2(x)−cos(x)​=0
g(x)f(x)​=0⇒f(x)=0−1+sin2(x)−cos(x)=0
Add cos(x) to both sides−1+sin2(x)=cos(x)
Square both sides(−1+sin2(x))2=cos2(x)
Subtract cos2(x) from both sides(−1+sin2(x))2−cos2(x)=0
Factor (−1+sin2(x))2−cos2(x):(−1+sin2(x)+cos(x))(−1+sin2(x)−cos(x))
(−1+sin2(x))2−cos2(x)
Apply Difference of Two Squares Formula: x2−y2=(x+y)(x−y)(−1+sin2(x))2−cos2(x)=((−1+sin2(x))+cos(x))((−1+sin2(x))−cos(x))=((−1+sin2(x))+cos(x))((−1+sin2(x))−cos(x))
Refine=(sin2(x)+cos(x)−1)(sin2(x)−cos(x)−1)
(−1+sin2(x)+cos(x))(−1+sin2(x)−cos(x))=0
Solving each part separately−1+sin2(x)+cos(x)=0or−1+sin2(x)−cos(x)=0
−1+sin2(x)+cos(x)=0:x=2π​+2πn,x=23π​+2πn,x=2πn
−1+sin2(x)+cos(x)=0
Rewrite using trig identities
−1+cos(x)+sin2(x)
Use the Pythagorean identity: 1=cos2(x)+sin2(x)1−sin2(x)=cos2(x)=cos(x)−cos2(x)
cos(x)−cos2(x)=0
Solve by substitution
cos(x)−cos2(x)=0
Let: cos(x)=uu−u2=0
u−u2=0:u=0,u=1
u−u2=0
Write in the standard form ax2+bx+c=0−u2+u=0
Solve with the quadratic formula
−u2+u=0
Quadratic Equation Formula:
For a=−1,b=1,c=0u1,2​=2(−1)−1±12−4(−1)⋅0​​
u1,2​=2(−1)−1±12−4(−1)⋅0​​
12−4(−1)⋅0​=1
12−4(−1)⋅0​
Apply rule 1a=112=1=1−4(−1)⋅0​
Apply rule −(−a)=a=1+4⋅1⋅0​
Apply rule 0⋅a=0=1+0​
Add the numbers: 1+0=1=1​
Apply rule 1​=1=1
u1,2​=2(−1)−1±1​
Separate the solutionsu1​=2(−1)−1+1​,u2​=2(−1)−1−1​
u=2(−1)−1+1​:0
2(−1)−1+1​
Remove parentheses: (−a)=−a=−2⋅1−1+1​
Add/Subtract the numbers: −1+1=0=−2⋅10​
Multiply the numbers: 2⋅1=2=−20​
Apply the fraction rule: −ba​=−ba​=−20​
Apply rule a0​=0,a=0=−0
=0
u=2(−1)−1−1​:1
2(−1)−1−1​
Remove parentheses: (−a)=−a=−2⋅1−1−1​
Subtract the numbers: −1−1=−2=−2⋅1−2​
Multiply the numbers: 2⋅1=2=−2−2​
Apply the fraction rule: −b−a​=ba​=22​
Apply rule aa​=1=1
The solutions to the quadratic equation are:u=0,u=1
Substitute back u=cos(x)cos(x)=0,cos(x)=1
cos(x)=0,cos(x)=1
cos(x)=0:x=2π​+2πn,x=23π​+2πn
cos(x)=0
General solutions for cos(x)=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​​​​
x=2π​+2πn,x=23π​+2πn
x=2π​+2πn,x=23π​+2πn
cos(x)=1:x=2πn
cos(x)=1
General solutions for cos(x)=1
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​​​​
x=0+2πn
x=0+2πn
Solve x=0+2πn:x=2πn
x=0+2πn
0+2πn=2πnx=2πn
x=2πn
Combine all the solutionsx=2π​+2πn,x=23π​+2πn,x=2πn
−1+sin2(x)−cos(x)=0:x=π+2πn,x=2π​+2πn,x=23π​+2πn
−1+sin2(x)−cos(x)=0
Rewrite using trig identities
−1−cos(x)+sin2(x)
Use the Pythagorean identity: 1=cos2(x)+sin2(x)1−sin2(x)=cos2(x)=−cos(x)−cos2(x)
−cos(x)−cos2(x)=0
Solve by substitution
−cos(x)−cos2(x)=0
Let: cos(x)=u−u−u2=0
−u−u2=0:u=−1,u=0
−u−u2=0
Write in the standard form ax2+bx+c=0−u2−u=0
Solve with the quadratic formula
−u2−u=0
Quadratic Equation Formula:
For a=−1,b=−1,c=0u1,2​=2(−1)−(−1)±(−1)2−4(−1)⋅0​​
u1,2​=2(−1)−(−1)±(−1)2−4(−1)⋅0​​
(−1)2−4(−1)⋅0​=1
(−1)2−4(−1)⋅0​
Apply rule −(−a)=a=(−1)2+4⋅1⋅0​
(−1)2=1
(−1)2
Apply exponent rule: (−a)n=an,if n is even(−1)2=12=12
Apply rule 1a=1=1
4⋅1⋅0=0
4⋅1⋅0
Apply rule 0⋅a=0=0
=1+0​
Add the numbers: 1+0=1=1​
Apply rule 1​=1=1
u1,2​=2(−1)−(−1)±1​
Separate the solutionsu1​=2(−1)−(−1)+1​,u2​=2(−1)−(−1)−1​
u=2(−1)−(−1)+1​:−1
2(−1)−(−1)+1​
Remove parentheses: (−a)=−a,−(−a)=a=−2⋅11+1​
Add the numbers: 1+1=2=−2⋅12​
Multiply the numbers: 2⋅1=2=−22​
Apply the fraction rule: −ba​=−ba​=−22​
Apply rule aa​=1=−1
u=2(−1)−(−1)−1​:0
2(−1)−(−1)−1​
Remove parentheses: (−a)=−a,−(−a)=a=−2⋅11−1​
Subtract the numbers: 1−1=0=−2⋅10​
Multiply the numbers: 2⋅1=2=−20​
Apply the fraction rule: −ba​=−ba​=−20​
Apply rule a0​=0,a=0=−0
=0
The solutions to the quadratic equation are:u=−1,u=0
Substitute back u=cos(x)cos(x)=−1,cos(x)=0
cos(x)=−1,cos(x)=0
cos(x)=−1:x=π+2πn
cos(x)=−1
General solutions for cos(x)=−1
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​​​​
x=π+2πn
x=π+2πn
cos(x)=0:x=2π​+2πn,x=23π​+2πn
cos(x)=0
General solutions for cos(x)=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​​​​
x=2π​+2πn,x=23π​+2πn
x=2π​+2πn,x=23π​+2πn
Combine all the solutionsx=π+2πn,x=2π​+2πn,x=23π​+2πn
Combine all the solutionsx=2π​+2πn,x=23π​+2πn,x=2πn,x=π+2πn
Verify solutions by plugging them into the original equation
Check the solutions by plugging them into cos(2π​−x)tan(x)−sec(−x)=1
Remove the ones that don't agree with the equation.
Check the solution 2π​+2πn:False
2π​+2πn
Plug in n=12π​+2π1
For cos(2π​−x)tan(x)−sec(−x)=1plug inx=2π​+2π1cos(2π​−(2π​+2π1))tan(2π​+2π1)−sec(−(2π​+2π1))=1
Undefined
⇒False
Check the solution 23π​+2πn:False
23π​+2πn
Plug in n=123π​+2π1
For cos(2π​−x)tan(x)−sec(−x)=1plug inx=23π​+2π1cos(2π​−(23π​+2π1))tan(23π​+2π1)−sec(−(23π​+2π1))=1
Undefined
⇒False
Check the solution 2πn:False
2πn
Plug in n=12π1
For cos(2π​−x)tan(x)−sec(−x)=1plug inx=2π1cos(2π​−2π1)tan(2π1)−sec(−2π1)=1
Refine−1=1
⇒False
Check the solution π+2πn:True
π+2πn
Plug in n=1π+2π1
For cos(2π​−x)tan(x)−sec(−x)=1plug inx=π+2π1cos(2π​−(π+2π1))tan(π+2π1)−sec(−(π+2π1))=1
Refine1=1
⇒True
x=π+2πn

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Frequently Asked Questions (FAQ)

  • What is the general solution for cos(pi/2-x)tan(x)-sec(-x)=1 ?

    The general solution for cos(pi/2-x)tan(x)-sec(-x)=1 is x=pi+2pin
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