6 ∫ x(x² + 3)² dx = 1 6 = .∫ (x² + 3)^2*(dx²) = 1 6 = .∫ (x² + 3)²*d(x²+3) = // make substitution/replacement x²+3 ---> t; 1 ---> 1^2+3 = 4; 6 ---> 6^2+3 = 39. You will get 1 39 = .∫ t^²*dt = // it is just an elementary integral from the tables 4 |39 = . | = . = 9875.833. |4