Askor mentioned: I thought trigonometric substitution only perform if there is offered a sq. root for example ##sqrt x^2 + 2 ##. No. Trig substitution is useful When you have the sum or distinction of squared conditions - they don't need to be within a square root. Impression of Glass https://gabletoppak.com/what-makes-gabletop-pak-cartons-a-better-choice-than-plastic-bottles/