Question

Найти неопределённый интеграл:

Answer 1

$\int (2x^2-1)cos(\frac{x}{3}) =\{u=2x^2-1,dU=cos(\frac{x}{3})\mid du=4x,U=3sin(\frac{x}{3})dx\}=\\\\=3sin(\frac{x}{3})(2x^2-1)-\int 12sin(\frac{x}{3})dx=3sin(\frac{x}{3})(2x^2-1)-12\int sin(\frac{x}{3})dx=\\\\=\{t=\frac{x}{3}, dt=\frac{1}{3}\}=>3sin(\frac{x}{3})(2x^2-1)-12\int 3sin(t)dt=3sin(\frac{x}{3})(2x^2-1)-\\\\-(12*(-3cos(\frac{x}{3})))=3sin(\frac{x}{3})(2x^2-1)+36cos(\frac{x}{3})+C$