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)

sin'(x) = cos(x)
cos'(x) = -sin(x)
tan'(x) = 1 + tan2(x)
sin'(f(x)) = cos(f(x)) · f'(x)
cos'(f(x)) = -sin(f(x)) · f'(x)
tan'(f(x)) = [1 + tan2(f(x))] · f'(x)
arcsin'(x) = 1 / √(1 - x2)
arccos'(x) = -1 / √(1 - x2)
arctan'(x) = 1 / (1 + x2)
arcsin'(f(x)) = f'(x) / √(1 - f(x)2)
arccos'(f(x)) = -f'(x) / √(1 - f(x)2)
arctan'(f(x)) = f'(x) / (1 + f(x)2)

log'(x) = 1 / x
log'(f(x)) = f'(x) / f(x)
logk'(x) = 1 / (x · ln(k))
logk'(f(x)) = f'(x) / (f(x) · ln(k))

ex' = ex
(ef(x))' = ef(x) · f'(x)
(kf(x))' = kf(x) · ln(k) · f'(x)
kx' = kx · ln(k)
[f(x)k]' = k · f(x)k-1 · f'(x)
xn' = nxn-1
Sum Rule:
D[f(x) + g(x)] = f'(x) + g'(x)
Constant Multiple Rule:
D[kf(x)] = kf'(x)
Product Rule:
D[f(x) · g(x)] = f'(x) · g(x) + f(x) · g'(x)
Quotient Rule:
D[f(x) / g(x)] = (f'(x) · g(x) - f(x) · g'(x)) / [g(x)]2
Chain Rule:
D(f[g(x)]) = f'[g(x)] · g'(x)
D(f(g[h(x)])) = f'(g[h(x)]) · g'(h(x)) · h'(x)
Power Rule
Trigonometric Derivatives:
D(sin(x)) = cos(x)
D[sin(f(x))] = f'(x) · cos(f(x))
D(cos(x)) = -sin(x)
D[cos(f(x))] = -f'(x) · sin(f(x))
D(tan(x)) = 1 + tan2(x)
D(tan(f(x))) = (1 + tan2(f(x))) · f'(x)
Exponential Derivatives:
D(ex) = ex
D[ef(x)] = ef(x) · f'(x)
D(ax) = ax · ln(a)
D[af(x)] = af(x) · ln(a) · f'(x)
Logarithmic Derivatives:

 

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