Askor stated: I thought trigonometric substitution only work if there is on the market a sq. root for instance ##sqrt x^2 + two ##. No. Trig substitution is helpful In case you have the sum or big difference of squared terms - they don't need to be inside a square https://gabletoppak.com/aseptic-tetra-pak-vs-non-aseptic-gable-top-choosing-the-right-carton-for-your-needs/