What are Trigonometric Identities?
In mathematics, an "identity" is an equation that is always true. These can be "trivially" true, like "x = x" or usefully true, such as the Pythagorean Theorem's "a2 + b2 = c2" for right triangles. Trigonometric identities are equations that relate to various trigonometric functions and are true for every variable value in the domain. Identity is essentially an equation that holds for all possible values of the variable(s) in it. Some algebraic identities are, for example, (a + b).
2 = a2 + 2ab + b2
(a - b)
2 = a2 - 2ab+ b2
(a + b)
(a-b)= a2 - b2
The algebraic identities only apply to the variables, but the trigonometric identities pertain to the six trigonometric functions sine, cosine, tangent, cosecant, secant, and cotangent. All of these and the rest of the types are described in detail in our Trigonometric Identities homework help service.
A Few Types of Trigonometric Identities
Reciprocal Trigonometric Identities
Sin, cosine, and tangent are reciprocals of cosecant, secant, and cotangent, respectively.As a result, the reciprocal identities are as follows:
- sin θ = 1/cosecθ (OR) cosec θ = 1/sinθ
- cos θ = 1/secθ (OR) sec θ = 1/cosθ
- tan θ = 1/cotθ (OR) cot θ = 1/tanθ
Pythagorean Trigonometric Identities
The Pythagorean trigonometric identities are derived from Pythagoras' theorem in trigonometry. By applying Pythagoras' theorem to the right-angled triangle below, we get:
- Opposite2 + Adjacent2 = Hypotenuse2
- Dividing both sides by Hypotenuse2
- Opposite2/Hypotenuse2+ Adjacent2/Hypotenuse2 = Hypotenuse2/Hypotenuse2
- sin2θ + cos2θ = 1
Similarly, we can derive two more Pythagorean trigonometric identities:
- 1 + tan2θ = sec2θ
- 1 + cot2θ = cosec2θ