Askor reported: I believed trigonometric substitution only do the job if there is available a sq. root for example ##sqrt x^two + two ##. No. Trig substitution is useful When you have the sum or difference of squared conditions - they don't need to be inside a sq. root. , https://gabletoppak.com/india-leads-in-generating-plastic-waste-with-10-2-mn-tonnes-a-year-study/