Askor said: I thought trigonometric substitution only work if there is on the market a square root for example ##sqrt x^two + 2 ##. No. Trig substitution is useful For those who have the sum or change of squared conditions - they don't need to be within a sq. root. https://gabletoppak.com/the-growing-threat-of-marine-pollution-and-how-gabletop-cartons-offer-a-solution/