Askor mentioned: I thought trigonometric substitution only do the job if there is on the market a square root like ##sqrt x^two + 2 ##. No. Trig substitution is useful When you have the sum or change of squared terms - they needn't be inside a square root. Gabletop Pak https://gabletoppak.com/why-i-switched-to-water-in-a-sustainable-box/