Askor stated: I thought trigonometric substitution only work if there is available a sq. root like ##sqrt x^two + two ##. No. Trig substitution is helpful In case you have the sum or difference of squared phrases - they needn't be inside of a square root. , or flat. From https://gabletoppak.com/sustainable-liquid-soap-packaging-why-gabletop-cartons-are-the-eco-friendly-choice/