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Signs of trigonometric functions in each quadrant. All Students Take Calculus is a mnemonic for the sign of each trigonometric functions in each quadrant of the plane. The letters ASTC signify which of the trigonometric functions are positive, starting in the top right 1st quadrant and moving counterclockwise through quadrants 2 to 4.
The mnemonic "SOHCAHTOA" (occasionally spelt "SOH CAH TOA") is often used to remember the basic trigonometric functions: [36] Sine = Opposite / Hypotenuse; Cosine = Adjacent / Hypotenuse; Tangent = Opposite / Adjacent; Other mnemonics that have been used for this include: Some Old Hippie Caught Another Hippie Tripping On Acid.
The Greeks focused on the calculation of chords, while mathematicians in India created the earliest-known tables of values for trigonometric ratios (also called trigonometric functions) such as sine. [3] Throughout history, trigonometry has been applied in areas such as geodesy, surveying, celestial mechanics, and navigation. [4]
Proof of the sum-and-difference-to-product cosine identity for prosthaphaeresis calculations using an isosceles triangle. The product-to-sum identities [28] or prosthaphaeresis formulae can be proven by expanding their right-hand sides using the angle addition theorems.
There are several equivalent ways for defining trigonometric functions, and the proofs of the trigonometric identities between them depend on the chosen definition. The oldest and most elementary definitions are based on the geometry of right triangles and the ratio between their sides.
As the historians L. Gauchet and Joseph Needham state, Guo Shoujing used spherical trigonometry in his calculations to improve the calendar system and Chinese astronomy. [ 30 ] [ 34 ] Along with a later 17th-century Chinese illustration of Guo's mathematical proofs, Needham states that:
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State of health (SoH) is a figure of merit of the condition of a battery (or a cell, or a battery pack), compared to its ideal conditions.The unit of SoH is percent (100% = the battery's conditions match the battery's specifications).