Askor said: I assumed trigonometric substitution only work if there is obtainable a square root including ##sqrt x^2 + two ##. No. Trig substitution is helpful When you have the sum or distinction of squared terms - they don't need to be inside a sq. root. , or flat. From https://gabletoppak.com/glass-bottles-for-beer-soda-and-even-water-found-to-contain-toxic-levels-of-cancer-linked-microplastics-than-plastic-bottles-study-says/