Askor said: I assumed trigonometric substitution only operate if there is obtainable a square root for instance ##sqrt x^2 + two ##. No. Trig substitution is helpful if you have the sum or change of squared phrases - they don't need to be within a sq. root. Gabletop Pak gives https://gabletoppak.com/from-plastic-bottles-to-gabletop-cartons-a-step-toward-solving-the-plastic-pollution-crisis/