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Cofunction, supplementary, quarter-turn, and reflection identities for the six trigonometric functions
Statement
For every real , and the quarter-turn and reflection formulas are On the common natural domains of the two sides, and The conventions and prerequisite facts used below are recorded in Pythagorean and parity identities for all six trigonometric functions on their natural domains, Quarter-turn values and shifts by pi/2 and pi, The addition formulas for sine and cosine, The zero sets of sine and cosine and the least positive common period 2 pi, Tangent, cotangent, secant, and cosecant on their exact natural domains.
Facts & Assumptions
Given: A real .
Quarter-turn values and shifts by pi/2 and pi states that, for every real , and .
The addition formulas for sine and cosine states that, for all real , and .
Tangent, cotangent, secant, and cosecant on their exact natural domains defines , , , and on their natural domains.
Proof
By [L1] with replaced by , and then [L3], and ; [L1] also gives the displayed quarter-turn formulas.
Apply [L2] to and use the values at supplied by [L1] (put ) together with [L3]. This gives and .
Substitute the cofunction and supplementary sine--cosine equalities into [L4]. The stated nonvanishing conditions are exactly those that make both quotient or reciprocal expressions defined, so this yields all eight displayed identities.
Depends on
- Pythagorean and parity identities for all six trigonometric functions on their natural domains
- Quarter-turn values and shifts by pi/2 and pi
- The addition formulas for sine and cosine
- The zero sets of sine and cosine and the least positive common period 2 pi
- Tangent, cotangent, secant, and cosecant on their exact natural domains
Used by
- Buffered certified rational phase approximation Algorithm
- A fixed Grover iteration count can fail when a is unknown Counterexample
- arcsin(sin x) is not the identity outside the principal interval Counterexample
- I₂(5) admits no crystallographic scaling and no reduced crystallographic root system with that base pairing Counterexample
- A prepared state with success amplitude one half Example
- Addition and half-angle identities compute the sine, cosine, and tangent of π/12 Example
- All meets and joins of the right weak order of A₂ (S₃), with the left order and the inversion sets compared Example
- B-tilde versus C-tilde: the n=2 coincidence and the duality behind the difference Example
- G2 from I2(6): the scaled realization and its twelve roots Example
- Machin's formula π/4=4 arctan(1/5)-arctan(1/239) Example
- Morrie's law: cos(π/9)cos(2π/9)cos(4π/9)=1/8 Example
- Quadratic Gauss sum at p=3 Example
- Quadratic Gauss sum at p=5 Example
- The A₂ root and weight lattices: P/Q has order three Example
- The arc length of one sine period is 4√2 E(1/√2) Example
- A Quantitative Logarithm Near the Identity in SU(2) Lemma
- Cartan-number products, allowed edge labels, tree scalings and reflection stability Lemma
- Continuous Markov derivative bound on an interval Lemma
- Efficient coherent amplitude-grid rounding Lemma
- Exact zero-label probability for counting Lemma
- Operator error for the finite sine-prefix rotation table Lemma
- Sine-window normalization and positive prefix weights Lemma
- The six exceptional Coxeter spectra: characteristic polynomials, orders and spectral exponents from exact matrices Lemma
- Two nearest phase labels carry probability at least eight over pi squared Lemma
- Amplitude-estimation additive error and success probability Theorem
- Classification of affine Coxeter diagrams and their Euclidean simplex realization Theorem
- Correctness and arithmetic resource bound for buffered phase approximation Theorem
- Known-amplitude success bound Theorem
- Principal arctangent: derivative, integral, power series, and the Gregory–Leibniz series Theorem
- Success bound under an explicit amplitude-amplification phase mismatch Theorem
- Success probability and repetition for modular order finding Theorem
Dependency tree · two levels
17 results within two dependency steps of this one, each drawn at its shortest distance from it. An arrow runs from a result to what uses it, so the chart reads left to right and ends at this result, which carries a heavier outline. Every node is a link to that result. Click elsewhere on the chart to enlarge it.
Sources
- NIST Digital Library of Mathematical Functions, Chapter 4 (standard reference, not scraped)