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Popular Trigonometry >

solvefor x,80=75-60cos(([pi*x])/(15))

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Solution

solvefor

Solution

x=π15⋅1.65422…​+30n,x=−π15⋅1.65422…​+30n
+1
Degrees
x=452.54208…∘+1718.87338…∘n,x=−452.54208…∘+1718.87338…∘n
Solution steps
80=75−60cos(15[πx]​)
Switch sides75−60cos(15[πx]​)=80
Move 75to the right side
75−60cos(15[πx]​)=80
Subtract 75 from both sides75−60cos(15[πx]​)−75=80−75
Simplify−60cos(15[πx]​)=5
−60cos(15[πx]​)=5
Divide both sides by −60
−60cos(15[πx]​)=5
Divide both sides by −60−60−60cos(15[πx]​)​=−605​
Simplify
−60−60cos(15[πx]​)​=−605​
Simplify −60−60cos(15[πx]​)​:cos(15[πx]​)
−60−60cos(15[πx]​)​
Apply the fraction rule: −b−a​=ba​=6060cos(15[πx]​)​
Divide the numbers: 6060​=1=cos(15[πx]​)
Simplify −605​:−121​
−605​
Apply the fraction rule: −ba​=−ba​=−605​
Cancel the common factor: 5=−121​
cos(15[πx]​)=−121​
cos(15[πx]​)=−121​
cos(15[πx]​)=−121​
Apply trig inverse properties
cos(15[πx]​)=−121​
General solutions for cos(15[πx]​)=−121​cos(x)=−a⇒x=arccos(−a)+2πn,x=−arccos(−a)+2πn15[πx]​=arccos(−121​)+2πn,15[πx]​=−arccos(−121​)+2πn
15[πx]​=arccos(−121​)+2πn,15[πx]​=−arccos(−121​)+2πn
Solve 15[πx]​=arccos(−121​)+2πn:x=π15arccos(−121​)​+30n
15[πx]​=arccos(−121​)+2πn
Multiply both sides by 15
15[πx]​=arccos(−121​)+2πn
Multiply both sides by 151515[πx]​=15arccos(−121​)+15⋅2πn
Simplify
1515[πx]​=15arccos(−121​)+15⋅2πn
Simplify 1515(πx)​:πx
1515[πx]​
Remove parentheses: (a)=a=1515πx​
Divide the numbers: 1515​=1=πx
Simplify 15arccos(−121​)+15⋅2πn:15arccos(−121​)+30πn
15arccos(−121​)+15⋅2πn
Multiply the numbers: 15⋅2=30=15arccos(−121​)+30πn
πx=15arccos(−121​)+30πn
πx=15arccos(−121​)+30πn
πx=15arccos(−121​)+30πn
Divide both sides by π
πx=15arccos(−121​)+30πn
Divide both sides by πππx​=π15arccos(−121​)​+π30πn​
Simplifyx=π15arccos(−121​)​+30n
x=π15arccos(−121​)​+30n
Solve 15[πx]​=−arccos(−121​)+2πn:x=−π15arccos(−121​)​+30n
15[πx]​=−arccos(−121​)+2πn
Multiply both sides by 15
15[πx]​=−arccos(−121​)+2πn
Multiply both sides by 151515[πx]​=−15arccos(−121​)+15⋅2πn
Simplify
1515[πx]​=−15arccos(−121​)+15⋅2πn
Simplify 1515(πx)​:πx
1515[πx]​
Remove parentheses: (a)=a=1515πx​
Divide the numbers: 1515​=1=πx
Simplify −15arccos(−121​)+15⋅2πn:−15arccos(−121​)+30πn
−15arccos(−121​)+15⋅2πn
Multiply the numbers: 15⋅2=30=−15arccos(−121​)+30πn
πx=−15arccos(−121​)+30πn
πx=−15arccos(−121​)+30πn
πx=−15arccos(−121​)+30πn
Divide both sides by π
πx=−15arccos(−121​)+30πn
Divide both sides by πππx​=−π15arccos(−121​)​+π30πn​
Simplifyx=−π15arccos(−121​)​+30n
x=−π15arccos(−121​)​+30n
x=π15arccos(−121​)​+30n,x=−π15arccos(−121​)​+30n
Show solutions in decimal formx=π15⋅1.65422…​+30n,x=−π15⋅1.65422…​+30n

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