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Trigonometry Angles--Pi/15


cos(pi/(15))=1/8(sqrt(30+6sqrt(5))+sqrt(5)-1)
(1)
cos((2pi)/(15))=1/8(sqrt(30-6sqrt(5))+sqrt(5)+1)
(2)
cos((4pi)/(15))=1/8(sqrt(30+6sqrt(5))-sqrt(5)+1)
(3)
cos((7pi)/(15))=1/8(sqrt(30-6sqrt(5))-sqrt(5)-1)
(4)
cot(pi/(15))=sqrt(7+2sqrt(5)+2sqrt(15+6sqrt(5)))
(5)
cot((2pi)/(15))=sqrt(7-2sqrt(5)+2sqrt(15-6sqrt(5)))
(6)
cot((4pi)/(15))=sqrt(7+2sqrt(5)-2sqrt(15+6sqrt(5)))
(7)
cot((7pi)/(15))=sqrt(7-2sqrt(5)-2sqrt(15-6sqrt(5)))
(8)
csc(pi/(15))=sqrt(8+2sqrt(5)+2sqrt(15+6sqrt(5)))
(9)
csc((2pi)/(15))=sqrt(8-2sqrt(5)+2sqrt(15-6sqrt(5)))
(10)
csc((4pi)/(15))=sqrt(8+2sqrt(5)-2sqrt(15+6sqrt(5)))
(11)
csc((7pi)/(15))=sqrt(8-2sqrt(5)-2sqrt(15-6sqrt(5)))
(12)
sec(pi/(15))=+2-sqrt(5)+sqrt(15-6sqrt(5))
(13)
sec((2pi)/(15))=-2-sqrt(5)+sqrt(15+6sqrt(5))
(14)
sec((4pi)/(15))=-2+sqrt(5)+sqrt(15-6sqrt(5))
(15)
sec((7pi)/(15))=+2+sqrt(5)+sqrt(15+6sqrt(5))
(16)
sin(pi/(15))=1/4sqrt(7-sqrt(5)-sqrt(30-6sqrt(5)))
(17)
sin((2pi)/(15))=1/4sqrt(7+sqrt(5)-sqrt(30+6sqrt(5)))
(18)
sin((4pi)/(15))=1/4sqrt(7-sqrt(5)+sqrt(30-6sqrt(5)))
(19)
sin((7pi)/(15))=1/4sqrt(7+sqrt(5)+sqrt(30+6sqrt(5)))
(20)
tan(pi/(15))=sqrt(23-10sqrt(5)-2sqrt(255-114sqrt(5)))
(21)
tan((2pi)/(15))=sqrt(23+10sqrt(5)-2sqrt(255+114sqrt(5)))
(22)
tan((4pi)/(15))=sqrt(23-10sqrt(5)+2sqrt(255-114sqrt(5)))
(23)
tan((7pi)/(15))=sqrt(23+10sqrt(5)+2sqrt(255+114sqrt(5))).
(24)

These can be derived using the trigonometric addition formulas

sin(pi/(15))=sin(pi/6-pi/(10))
(25)
=sin(pi/6)cos(pi/(10))-sin(pi/(10))cos(pi/6)
(26)
=1/2sqrt(1/8(5+sqrt(5)))-(sqrt(3))/2··1/4(sqrt(5)-1)
(27)
=1/(16)(2sqrt(3)-2sqrt(15)+sqrt(40+8sqrt(5)))
(28)

and

cos(pi/(15))=cos(pi/6-pi/(10))
(29)
=cos(pi/6)cos(pi/(10))+sin(pi/6)sin(pi/(10))
(30)
=(sqrt(3))/2sqrt(1/8(5+sqrt(5)))+1/2·1/4(sqrt(5)-1)
(31)
=1/8(sqrt(30+6sqrt(5))+sqrt(5)-1).
(32)

See also

Pentadecagon, Trigonometry Angles, Trigonometry, Trigonometry Angles--Pi/6, Trigonometry Angles--Pi/10

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Cite this as:

Weisstein, Eric W. "Trigonometry Angles--Pi/15." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/TrigonometryAnglesPi15.html

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