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Trigonometry Angles--Pi/10


cos(pi/(10))=1/4sqrt(10+2sqrt(5))
(1)
cos((3pi)/(10))=1/4sqrt(10-2sqrt(5))
(2)
cot(pi/(10))=sqrt(5+2sqrt(5))
(3)
cot((3pi)/(10))=sqrt(5-2sqrt(5))
(4)
csc(pi/(10))=1+sqrt(5)
(5)
csc((3pi)/(10))=sqrt(5)-1
(6)
sec(pi/(10))=1/5sqrt(50-10sqrt(5))
(7)
sec((3pi)/(10))=1/5sqrt(50+10sqrt(5))
(8)
sin(pi/(10))=1/4(sqrt(5)-1)
(9)
sin((3pi)/(10))=1/4(1+sqrt(5))
(10)
tan(pi/(10))=1/5sqrt(25-10sqrt(5))
(11)
tan((3pi)/(10))=1/5sqrt(25+10sqrt(5)).
(12)

To derive these formulas, use the half-angle formulas

sin(pi/(10))=sin(1/2·pi/5)
(13)
=sqrt(1/2[1-cos(pi/5)])
(14)
=sqrt(1/2[1-1/4(1+sqrt(5))])
(15)
=1/4(sqrt(5)-1)
(16)
cos(pi/(10))=cos(1/2·pi/5)
(17)
=sqrt(1/2[1+cos(pi/5)])
(18)
=sqrt(1/2[1+1/4(1+sqrt(5))])
(19)
=1/4sqrt(10+2sqrt(5))
(20)
tan(pi/(10))=sqrt((3-sqrt(5))/(5+sqrt(5)))
(21)
=1/5sqrt(25-10sqrt(5)).
(22)

See also

Decagon, Decagram, Trigonometry Angles, Trigonometry, Trigonometry Angles--Pi/5

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Cite this as:

Weisstein, Eric W. "Trigonometry Angles--Pi/10." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/TrigonometryAnglesPi10.html

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