trigonometric substitutions

trigonometric substitutions

[¦trig·ə·nə¦me·trik ‚səb·stə′tü·shənz]
(mathematics)
The substitutions x = a sin u, x = a tan u, and x = a sec u, which are used to rationalize expressions of the form √(a 2-x 2), √(x 2+ a 2), and √(x 2-a 2), respectively, when they appear in integrals.