You're browsing as a guest. Sign up to study, save and track progress.
mathematicstrigonometryformulas
Trigonometric identities
The identities worth knowing by heart, from Pythagoras to the laws of triangles.
13 cards
FrontBackTags
sin²x + cos²x
1pythagorean
1 + tan²xDivide the Pythagorean identity by cos²x.
sec²xpythagorean
1 + cot²xDivide the Pythagorean identity by sin²x.
csc²xpythagorean
sin 2x
2 sin x cos xdouble-angle
cos 2x
cos²x − sin²xdouble-angle
tan 2x
2 tan x / (1 − tan²x)double-angle
sin(a ± b)
sin a cos b ± cos a sin bsum-difference
cos(a ± b)The sign flips.
cos a cos b ∓ sin a sin bsum-difference
tan(a + b)
(tan a + tan b) / (1 − tan a tan b)sum-difference
sin²x
(1 − cos 2x) / 2power-reduction
cos²x
(1 + cos 2x) / 2power-reduction
Law of sines
a / sin A = b / sin B = c / sin Ctriangle
Law of cosines
c² = a² + b² − 2ab cos Ctriangle