Askor said: I thought trigonometric substitution only function if there is on the market a square root for instance ##sqrt x^two + two ##. No. Trig substitution is useful if you have the sum or big difference of squared terms - they don't need to be inside a sq. root. https://gabletoppak.com/bioplastics-greenwashing-or-genuine-solution-the-truth-behind-the-hype/