Essential Trigonometric Identities and Formulas
Classified in Mathematics
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Pythagorean Identities:
sin (a + b) = sin(a) · cos(b) + cos(a) · sin(b) cos (a + b) = cos(a) · cos(b) - sin(a) · sin(b) tan (a + b) = (tan(a) + tan(b)) / (1 - tan(a)tan(b)) sin(2a) = 2 · sin(a) · cos(a) cos(2a) = cos2(a) - sin2(a) tan(2a) = 2tan(a) / (1 - tan2(a)) sin(a / 2) = ±√((1 - cos(a)) / 2) cos(a / 2) = ±√((1 + cos(a)) / 2) tan(a / 2) = ±√((1 - cos(a)) / (1 + cos(a))) sin(a)sin(b) = 2sin((a + b) / 2) · cos((a - b) / 2) sin(a) - sin(b) = 2cos((a + b) / 2) · sin((a - b) / 2) cos(a) + cos(b) = 2cos((a + b) / 2) · cos((a - b) / 2) cos(a) - cos(b) = -2sin((a + b) / 2) · sin((a - b) / 2) |
Basic Trigonometric Identities:
sin2(x) + cos2(x) = 1 1 + tan2(x) = sec2(x) 1 + cot2(x) = csc2(x) tan(x) = sin(x) / cos(x) csc(x) = 1 / sin(x) sec(x) = 1 / cos(x) cot(x) = 1 / tan(x) = cos(x) / sin(x) 1 + cot2(a) = csc2(a) sin (a + b) = sin(a) · cos(b) + cos(a) · sin(b) cos (a + b) = cos(a) · cos(b) - sin(a) · sin(b) sin (a - b) = sin(a) · cos(b) - cos(a) · sin(b) cos (a - b) = cos(a) · cos(b) + sin(a) · sin(b) sin(2a) = 2sin(a) · cos(a) cos(2a) = cos2(a) - sin2(a) tan(2a) = 2tan(a) / (1 - tan2(a)) sin (a / 2) = ±√((1 - cos(a)) / 2) cos (a / 2) = ±√((1 + cos(a)) / 2) tan (a / 2) = ±√((1 - cos(a)) / (1 + cos(a))) sin(a) + sin(b) = 2 · sin((a + b) / 2) · cos((a - b) / 2) sin(a) - sin(b) = 2 · cos((a + b) / 2) · sin((a - b) / 2) cos(a) + cos(b) = 2 · cos((a + b) / 2) · cos((a - b) / 2) cos(a) - cos(b) = -2 · sin((a + b) / 2) · sin((a - b) / 2) cos(a) = adjacent / hypotenuse => sec(a) sin(a) = opposite / hypotenuse => csc(a) tan(a) = opposite / adjacent => cotangent(a) = sin(a) / cos(a) |
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