Askor stated: I assumed trigonometric substitution only do the job if there is out there a sq. root for example ##sqrt x^2 + two ##. No. Trig substitution is useful In case you have the sum or change of squared terms - they need not be within a sq. root. https://gabletoppak.com/best-alternatives-to-plastic-water-bottles-in-kerala-for-a-greener-future/