Askor claimed: I assumed trigonometric substitution only work if there is on the market a square root including ##sqrt x^2 + two ##. No. Trig substitution is useful When you have the sum or big difference of squared terms - they don't need to be inside of a square root. https://gabletoppak.com/india-leads-in-generating-plastic-waste-with-10-2-mn-tonnes-a-year-study/