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- An identity is a true mathematical equation, e.g. 5(x+1)=5x+5
- A trigonometric identity is an identity with trigonometric expressions
- Fundamental Trigonometric Identities
- Quotient Identity: sin x/cos x = tan x
- Pythagorean Identity:
- sin2x+cos2x=1
- sin2x=1-cos2x
- cos2x=1-sin2x
For a triangle ∆ABC with sides a, b, and c.
C
b
a
A
B
c
- The Sine Law
- a/sin A = b/sin B = c/sin C
sin
A/a = sin B/b = sin C/c
- The Cosine Law
- a2 = b2 + c2 - 2bc cos A
- b2 = a2 + c2 - 2ac cos B
- c2 = a2 + b2 - 2ab cos C
An oblique triangle is a triangle without a right angle
acute, right obtuse