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Popular Trigonometry >

cos(x+10)-cos(x+90)=1

  • Pre Algebra
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Solution

cos(x+10∘)−cos(x+90∘)=1

Solution

x=−50∘+360∘n+0.89125…,x=130∘+360∘n−0.89125…
+1
Radians
x=−185π​+0.89125…+2πn,x=1813π​−0.89125…+2πn
Solution steps
cos(x+10∘)−cos(x+90∘)=1
Rewrite using trig identities
cos(x+10∘)−cos(x+90∘)
Use the Sum to Product identity: cos(s)−cos(t)=−2sin(2s+t​)sin(2s−t​)=−2sin(2x+10∘+x+90∘​)sin(2x+10∘−(x+90∘)​)
Simplify −2sin(2x+10∘+x+90∘​)sin(2x+10∘−(x+90∘)​):2sin(40∘)sin(1818x+900∘​)
−2sin(2x+10∘+x+90∘​)sin(2x+10∘−(x+90∘)​)
2x+10∘+x+90∘​=1818x+900∘​
2x+10∘+x+90∘​
x+10∘+x+90∘=2x+90∘+10∘
x+10∘+x+90∘
Group like terms=x+x+90∘+10∘
Add similar elements: x+x=2x=2x+90∘+10∘
=22x+90∘+10∘​
Join 2x+90∘+10∘:918x+900∘​
2x+90∘+10∘
Convert element to fraction: 2x=12x​=12x​+90∘+10∘
Least Common Multiplier of 1,2,18:18
1,2,18
Least Common Multiplier (LCM)
Prime factorization of 1
Prime factorization of 2:2
2
2 is a prime number, therefore no factorization is possible=2
Prime factorization of 18:2⋅3⋅3
18
18divides by 218=9⋅2=2⋅9
9divides by 39=3⋅3=2⋅3⋅3
2,3 are all prime numbers, therefore no further factorization is possible=2⋅3⋅3
Compute a number comprised of factors that appear in at least one of the following:
1,2,18
=2⋅3⋅3
Multiply the numbers: 2⋅3⋅3=18=18
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 18
For 12x​:multiply the denominator and numerator by 1812x​=1⋅182x⋅18​=1836x​
For 90∘:multiply the denominator and numerator by 990∘=2⋅9180∘9​=90∘
=1836x​+90∘+10∘
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=1836x+180∘9+180∘​
Add similar elements: 1620∘+180∘=1800∘=1836x+1800∘​
Factor 36x+1800∘:2(18x+900∘)
36x+1800∘
Rewrite as=2⋅18x+2⋅900∘
Factor out common term 2=2(18x+900∘)
=182(18x+900∘)​
Cancel the common factor: 2=918x+900∘​
=2918x+900∘​​
Apply the fraction rule: acb​​=c⋅ab​=9⋅218x+900∘​
Multiply the numbers: 9⋅2=18=1818x+900∘​
=−2sin(1818x+900∘​)sin(2x−(x+90∘)+10∘​)
2x+10∘−(x+90∘)​=−40∘
2x+10∘−(x+90∘)​
Join x+10∘−(x+90∘):−80∘
x+10∘−(x+90∘)
Convert element to fraction: x=18x18​,(x+90∘)=18(x+90∘)18​=18x⋅18​+10∘−18(x+90∘)⋅18​
Since the denominators are equal, combine the fractions: ca​±cb​=ca±b​=18x⋅18+180∘−(x+90∘)⋅18​
Expand x⋅18+180∘−(x+90∘)⋅18:−1440∘
x⋅18+180∘−(x+90∘)⋅18
=18x+180∘−18(x+90∘)
Expand −18(x+90∘):−18x−1620∘
−18(x+90∘)
Apply the distributive law: a(b+c)=ab+aca=−18,b=x,c=90∘=−18x+(−18)90∘
Apply minus-plus rules+(−a)=−a=−18x−18⋅90∘
18⋅90∘=1620∘
18⋅90∘
Multiply fractions: a⋅cb​=ca⋅b​=1620∘
Divide the numbers: 218​=9=1620∘
=−18x−1620∘
=x⋅18+180∘−18x−1620∘
Simplify x⋅18+180∘−18x−1620∘:−1440∘
x⋅18+180∘−18x−1620∘
Group like terms=18x−18x+180∘−1620∘
Add similar elements: 18x−18x=0=180∘−1620∘
Add similar elements: 180∘−1620∘=−1440∘=−1440∘
=−1440∘
=18−1440∘​
Apply the fraction rule: b−a​=−ba​=−80∘
Cancel the common factor: 2=−80∘
=2−80∘​
Apply the fraction rule: b−a​=−ba​=−280∘​
Apply the fraction rule: acb​​=c⋅ab​280∘​=9⋅2720∘​=−9⋅2720∘​
Multiply the numbers: 9⋅2=18=−40∘
Cancel the common factor: 2=−40∘
=−2sin(−40∘)sin(1818x+900∘​)
Simplify sin(−40∘):−sin(40∘)
sin(−40∘)
Use the following property: sin(−x)=−sin(x)sin(−40∘)=−sin(40∘)=−sin(40∘)
=−2(−sin(40∘))sin(1818x+900∘​)
Apply rule −(−a)=a=2sin(1818x+900∘​)sin(40∘)
=2sin(40∘)sin(1818x+900∘​)
2sin(40∘)sin(1818x+900∘​)=1
Divide both sides by 2sin(40∘)
2sin(40∘)sin(1818x+900∘​)=1
Divide both sides by 2sin(40∘)2sin(40∘)2sin(40∘)sin(1818x+900∘​)​=2sin(40∘)1​
Simplifysin(1818x+900∘​)=2sin(40∘)1​
sin(1818x+900∘​)=2sin(40∘)1​
Apply trig inverse properties
sin(1818x+900∘​)=2sin(40∘)1​
General solutions for sin(1818x+900∘​)=2sin(40∘)1​sin(x)=a⇒x=arcsin(a)+360∘n,x=180∘−arcsin(a)+360∘n1818x+900∘​=arcsin(2sin(40∘)1​)+360∘n,1818x+900∘​=180∘−arcsin(2sin(40∘)1​)+360∘n
1818x+900∘​=arcsin(2sin(40∘)1​)+360∘n,1818x+900∘​=180∘−arcsin(2sin(40∘)1​)+360∘n
Solve 1818x+900∘​=arcsin(2sin(40∘)1​)+360∘n:x=−50∘+360∘n+arcsin(2sin(40∘)1​)
1818x+900∘​=arcsin(2sin(40∘)1​)+360∘n
Multiply both sides by 18
1818x+900∘​=arcsin(2sin(40∘)1​)+360∘n
Multiply both sides by 181818(18x+900∘)​=18arcsin(2sin(40∘)1​)+18⋅360∘n
Simplify
1818(18x+900∘)​=18arcsin(2sin(40∘)1​)+18⋅360∘n
Simplify 1818(18x+900∘)​:18x+900∘
1818(18x+900∘)​
Divide the numbers: 1818​=1=18x+900∘
Simplify 18arcsin(2sin(40∘)1​)+18⋅360∘n:18arcsin(2sin(40∘)1​)+6480∘n
18arcsin(2sin(40∘)1​)+18⋅360∘n
Multiply the numbers: 18⋅2=36=18arcsin(2sin(40∘)1​)+6480∘n
18x+900∘=18arcsin(2sin(40∘)1​)+6480∘n
18x+900∘=18arcsin(2sin(40∘)1​)+6480∘n
18x+900∘=18arcsin(2sin(40∘)1​)+6480∘n
Move 900∘to the right side
18x+900∘=18arcsin(2sin(40∘)1​)+6480∘n
Subtract 900∘ from both sides18x+900∘−900∘=18arcsin(2sin(40∘)1​)+6480∘n−900∘
Simplify18x=18arcsin(2sin(40∘)1​)+6480∘n−900∘
18x=18arcsin(2sin(40∘)1​)+6480∘n−900∘
Divide both sides by 18
18x=18arcsin(2sin(40∘)1​)+6480∘n−900∘
Divide both sides by 181818x​=1818arcsin(2sin(40∘)1​)​+186480∘n​−50∘
Simplify
1818x​=1818arcsin(2sin(40∘)1​)​+186480∘n​−50∘
Simplify 1818x​:x
1818x​
Divide the numbers: 1818​=1=x
Simplify 1818arcsin(2sin(40∘)1​)​+186480∘n​−50∘:−50∘+360∘n+arcsin(2sin(40∘)1​)
1818arcsin(2sin(40∘)1​)​+186480∘n​−50∘
Group like terms=−50∘+186480∘n​+1818arcsin(2sin(40∘)1​)​
Divide the numbers: 1836​=2=−50∘+360∘n+1818arcsin(2sin(40∘)1​)​
Divide the numbers: 1818​=1=−50∘+360∘n+arcsin(2sin(40∘)1​)
x=−50∘+360∘n+arcsin(2sin(40∘)1​)
x=−50∘+360∘n+arcsin(2sin(40∘)1​)
x=−50∘+360∘n+arcsin(2sin(40∘)1​)
Solve 1818x+900∘​=180∘−arcsin(2sin(40∘)1​)+360∘n:x=130∘+360∘n−arcsin(2sin(40∘)1​)
1818x+900∘​=180∘−arcsin(2sin(40∘)1​)+360∘n
Multiply both sides by 18
1818x+900∘​=180∘−arcsin(2sin(40∘)1​)+360∘n
Multiply both sides by 181818(18x+900∘)​=3240∘−18arcsin(2sin(40∘)1​)+18⋅360∘n
Simplify
1818(18x+900∘)​=3240∘−18arcsin(2sin(40∘)1​)+18⋅360∘n
Simplify 1818(18x+900∘)​:18x+900∘
1818(18x+900∘)​
Divide the numbers: 1818​=1=18x+900∘
Simplify 3240∘−18arcsin(2sin(40∘)1​)+18⋅360∘n:3240∘−18arcsin(2sin(40∘)1​)+6480∘n
3240∘−18arcsin(2sin(40∘)1​)+18⋅360∘n
Multiply the numbers: 18⋅2=36=3240∘−18arcsin(2sin(40∘)1​)+6480∘n
18x+900∘=3240∘−18arcsin(2sin(40∘)1​)+6480∘n
18x+900∘=3240∘−18arcsin(2sin(40∘)1​)+6480∘n
18x+900∘=3240∘−18arcsin(2sin(40∘)1​)+6480∘n
Move 900∘to the right side
18x+900∘=3240∘−18arcsin(2sin(40∘)1​)+6480∘n
Subtract 900∘ from both sides18x+900∘−900∘=3240∘−18arcsin(2sin(40∘)1​)+6480∘n−900∘
Simplify
18x+900∘−900∘=3240∘−18arcsin(2sin(40∘)1​)+6480∘n−900∘
Simplify 18x+900∘−900∘:18x
18x+900∘−900∘
Add similar elements: 900∘−900∘=0
=18x
Simplify 3240∘−18arcsin(2sin(40∘)1​)+6480∘n−900∘:2340∘+6480∘n−18arcsin(2sin(40∘)1​)
3240∘−18arcsin(2sin(40∘)1​)+6480∘n−900∘
Group like terms=3240∘−900∘+6480∘n−18arcsin(2sin(40∘)1​)
Add similar elements: 3240∘−900∘=2340∘=2340∘+6480∘n−18arcsin(2sin(40∘)1​)
18x=2340∘+6480∘n−18arcsin(2sin(40∘)1​)
18x=2340∘+6480∘n−18arcsin(2sin(40∘)1​)
18x=2340∘+6480∘n−18arcsin(2sin(40∘)1​)
Divide both sides by 18
18x=2340∘+6480∘n−18arcsin(2sin(40∘)1​)
Divide both sides by 181818x​=130∘+186480∘n​−1818arcsin(2sin(40∘)1​)​
Simplify
1818x​=130∘+186480∘n​−1818arcsin(2sin(40∘)1​)​
Simplify 1818x​:x
1818x​
Divide the numbers: 1818​=1=x
Simplify 130∘+186480∘n​−1818arcsin(2sin(40∘)1​)​:130∘+360∘n−arcsin(2sin(40∘)1​)
130∘+186480∘n​−1818arcsin(2sin(40∘)1​)​
Divide the numbers: 1836​=2=130∘+360∘n−1818arcsin(2sin(40∘)1​)​
Divide the numbers: 1818​=1=130∘+360∘n−arcsin(2sin(40∘)1​)
x=130∘+360∘n−arcsin(2sin(40∘)1​)
x=130∘+360∘n−arcsin(2sin(40∘)1​)
x=130∘+360∘n−arcsin(2sin(40∘)1​)
x=−50∘+360∘n+arcsin(2sin(40∘)1​),x=130∘+360∘n−arcsin(2sin(40∘)1​)
Show solutions in decimal formx=−50∘+360∘n+0.89125…,x=130∘+360∘n−0.89125…

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Frequently Asked Questions (FAQ)

  • What is the general solution for cos(x+10)-cos(x+90)=1 ?

    The general solution for cos(x+10)-cos(x+90)=1 is x=-50+360n+0.89125…,x=130+360n-0.89125…
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