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The proofs given in this article use these definitions, and thus apply to non-negative angles not greater than a right angle. For greater and negative angles , see Trigonometric functions . Other definitions, and therefore other proofs are based on the Taylor series of sine and cosine , or on the differential equation f ″ + f = 0 ...
There are a number of ways to demonstrate the validity of the small-angle approximations. The most direct method is to truncate the Maclaurin series for each of the trigonometric functions. Depending on the order of the approximation , cos θ {\displaystyle \textstyle \cos \theta } is approximated as either 1 {\displaystyle 1} or as 1 − 1 ...
A formula for computing the trigonometric identities for the one-third angle exists, but it requires finding the zeroes of the cubic equation 4x 3 − 3x + d = 0, where is the value of the cosine function at the one-third angle and d is the known value of the cosine function at the full angle.
We conclude that for 0 < θ < 1 / 2 π, the quantity sin(θ)/θ is always less than 1 and always greater than cos(θ). Thus, as θ gets closer to 0, sin(θ)/θ is "squeezed" between a ceiling at height 1 and a floor at height cos θ, which rises towards 1; hence sin(θ)/θ must tend to 1 as θ tends to 0 from the positive side:
To prove the law of tangents one can start with the law of sines: a sin α = b sin β = d , {\displaystyle {\frac {a}{\sin \alpha }}={\frac {b}{\sin \beta }}=d,} where d {\displaystyle d} is the diameter of the circumcircle , so that a = d sin α {\displaystyle a=d\sin \alpha } and b = d sin β {\displaystyle ...
Then by the triple-angle formula, cos π / 3 = 4x 3 − 3x and so 4x 3 − 3x = 1 / 2 . Thus 8x 3 − 6x − 1 = 0. Define p(t) to be the polynomial p(t) = 8t 3 − 6t − 1. Since x = cos 20° is a root of p(t), the minimal polynomial for cos 20° is a factor of p(t). Because p(t) has degree 3, if it is reducible over by Q then ...
Proofs of the mathematical result that the rational number 22 / 7 is greater than π (pi) date back to antiquity. One of these proofs, more recently developed but requiring only elementary techniques from calculus, has attracted attention in modern mathematics due to its mathematical elegance and its connections to the theory of Diophantine approximations.
If one wishes to prove a statement, not for all natural numbers, but only for all numbers n greater than or equal to a certain number b, then the proof by induction consists of the following: Showing that the statement holds when n = b. Showing that if the statement holds for an arbitrary number n ≥ b, then the same statement also holds for n ...