The right triangle ABC has sides of length x and y, and hypotenuse of length h. The tangent ratio of angle A is the opposite side over the adjacent side, so {eq}\tan A = \frac {y} {x} {/eq}. The
The Pythagorean identities are based on the properties of a right triangle. cos2θ + sin2θ = 1. 1 + cot2θ = csc2θ. 1 + tan2θ = sec2θ. The even-odd identities relate the value of a trigonometric function at a given angle to the value of the function at the opposite angle. tan( − θ) = − tanθ. cot( − θ) = − cotθ.
Theorem: Law of Tangents. If a triangle has sides of lengths a, b, and c opposite the angles A, B, and C, respectively, then. (2.3.1) a − b a + b = tan 1 2 ( A − B) tan 1 2 ( A + B) , (2.3.2) b − c b + c = tan 1 2 ( B − C) tan 1 2 ( B + C) , (2.3.3) c − a c + a = tan 1 2 ( C − A) tan 1 2 ( C + A) . Note that since tan ( − θ
tan θ ≈ θ at about 0.1730 radians (9.91°) sin θ ≈ θ at about 0.2441 radians (13.99°) cos θ ≈ 1 − θ 2 / 2 at about 0.6620 radians (37.93°) Angle sum and difference. The angle addition and subtraction theorems reduce to the following when one of the angles is small (β ≈ 0): 1uE5.