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Maths Exercices
Trigonometric identities

The following equations are the most basic and important trigonometric identities. These equations are true for any angle. From them, countless additional identities can be formed.

Basic trigonometric identities:

tanθ = sinθ
  cotθ = _1_
  secθ = _1_
  cscθ = _1_

triángulo Pythagorean Identities:
a) sin2A + cos2 A = 1

b) 1 + tg2 A = sec2A
c) 1 + cot2 A = csc2A

You can use the trigonometric identities given above to find trigonometric ratios if you are given the quadrant an angle lies in and the value of one trigonometric ratio.

It will be useful to remember the sign of the trigonometric ratios in each quadrant:


If sinθ= and , find cosθ and tanθ.

cos2θ=1-sin2θ=1-()2=, then cosθ=- because

If the cotangent of an angle is -1.555 and the angle is in the fourth quadrant

Find the trigonometric ratios asked:

Sine = Secant =
(round the solution to thousandths)