The fundamental Pythagorean identity is
(1)
It follows from the Pythagorean theorem applied to a point on the unit circle . Dividing by
(2)
and
(3)
The last two identities hold wherever all of their trigonometric
functions are defined.
See also Cosecant ,
Cosine ,
Cotangent ,
Pythagorean
Theorem ,
Secant ,
Sine ,
Tangent
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References Zwillinger, D. (Ed.). CRC Standard Mathematical Tables and Formulae, 33rd ed.
Cite this as:
Weisstein, Eric W. "Pythagorean Identity."
From MathWorld https://mathworld.wolfram.com/PythagoreanIdentity.html
Subject classifications
or 
, respectively, gives the two related Pythagorean
identities
