Askor mentioned: I believed trigonometric substitution only do the job if there is available a square root which include ##sqrt x^2 + 2 ##. No. Trig substitution is helpful For those who have the sum or difference of squared terms - they don't need to be inside a square root. https://gabletoppak.com/why-gable-top-cartons-are-making-a-splash-in-the-water-industry/