This paper presents a simpler and shorter method of evaluating integrals of powers of sine. The reduction formula for sine is repeatedly applied to the integral of the nth power of sine until generalized formulas are derived. Since the derivation process involves recursive relations, the coefficients and exponents of the derived formulas showed certain patterns and sequences which were used as the basis for developing an easier algorithm.Key words: Integration, mathematical algorithm, powers of sine, reduction formula, trigonometric identities.
IntroductionEvaluating integrals of powers of trigonometric functions is always part of the study of Integral Calculus. Integrals of powers of sine are usually evaluated using trigonometric identities and the solution depends on whether the power is odd or even. For odd powers, the integrand is transformed by factoring out one sine and the remaining even powered sine is converted into cosine using the identity Another method used to evaluate powers of sine is by using reduction formula. A reduction formula transforms the integral into an integral of the same or similar expression with a lower integer exponent [4]. It is repeatedly applied until the power of the last term is reduced to two or one, and the final integral can be evaluated. Using integration by parts, the reduction formula for sine is [5].
The methods discussed above are normally tedious and time consuming depending on the given power of sine. As shown in the study of Dampil [6], deriving generalized formulas can simplify solutions, hence, the objective of this paper is to come up with a shorter and simpler method of integrating powers of sine. Generalized formulas are derived by successive application of the reduction formula to the integral of the nth power of sine. Because of the recursive nature of the reduction formula, an algorithm is developed
International Journal of Applied Physics and Mathematics
192Volume 5, Number 3, July 2015Lito E. Suello* Malayan Colleges Laguna, Pulo-Diezmo Road, Cabuyao City, Laguna, Philippines.Manuscript submitted January 25, 2015; accepted June 5, 2015.* Corresponding author. Tel.: +639497688588; email: lesuello@mcl.edu.ph based on the sequences and patterns of the coefficients and exponents of the terms of the derived formulas.