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Terms with infinitely many sine factors would necessarily be equal to zero. When only finitely many of the angles are nonzero then only finitely many of the terms on the right side are nonzero because all but finitely many sine factors vanish. Furthermore, in each term all but finitely many of the cosine factors are unity.
Similarly / = is a constructible angle because 12 is a power of two (4) times a Fermat prime (3). But π / 9 = 20 ∘ {\displaystyle \pi /9=20^{\circ }} is not a constructible angle, since 9 = 3 ⋅ 3 {\displaystyle 9=3\cdot 3} is not the product of distinct Fermat primes as it contains 3 as a factor twice, and neither is π / 7 ≈ 25.714 ∘ ...
In this right triangle, denoting the measure of angle BAC as A: sin A = a / c ; cos A = b / c ; tan A = a / b . Plot of the six trigonometric functions, the unit circle, and a line for the angle θ = 0.7 radians. The points labeled 1, Sec(θ), Csc(θ) represent the length of the line segment from the origin to that point.
Many slide rules – especially "trig" and higher models – include an "ST" (sines and tangents) or "SRT" (sines, radians, and tangents) scale on the front or back of the slide, for computing with trigonometric functions of angles smaller than about 0.1 radian (or within about 0.1 radian of /, that is, within 5.7 degrees of 90 degrees, in the ...
The sign of the square root needs to be chosen properly—note that if 2 π is added to θ, the quantities inside the square roots are unchanged, but the left-hand-sides of the equations change sign. Therefore, the correct sign to use depends on the value of θ. For the tan function, the equation is:
On the unit sphere, this radian measure is numerically equal to the arc length. By convention, the sides of proper spherical triangles are less than π , so that 0 < a + b + c < 2 π {\displaystyle 0<a+b+c<2\pi } (Todhunter, [ 1 ] Art.22,32).
Quadrant 1 (angles from 0 to 90 degrees, or 0 to π/2 radians): All trigonometric functions are positive in this quadrant. Quadrant 2 (angles from 90 to 180 degrees, or π/2 to π radians): S ine and cosecant functions are positive in this quadrant.
The angle opposite the leg of length 1 (this angle can be labeled φ = π/2 − θ) has cotangent equal to the length of the other leg, and cosecant equal to the length of the hypotenuse. In that way, this trigonometric identity involving the cotangent and the cosecant also follows from the Pythagorean theorem.