int 2x^3cos(x^2) dx Find the indefinite integral by using substitution followed by integration by parts.
Recall that indefinite integral follows int f(x) dx = F(x) +C where: f(x) as the integrand function F(x) as the antiderivative of f(x) C as the constant of integration. For the given integral problem: int 2x^3 cos(x^2) dx , we may apply apply u-substitution by letting: u = x^2 then du =2x dx . Note that x^3 =x^2 *x then 2x^3 dx = 2*x^2 *x dx or x^2 * 2x dx The integral becomes: int 2x^3 cos(x^2) dx =int x^2 *cos(x^2) *2x dx = int u cos(u) du Apply formula of integration by parts: int f*g'=f*g - int g*f' . Let: f =u then f' =du g' =cos(u) du then g=sin(u) Note: From the table of integrals, we have int cos(x) dx =sin(x) +C . int u *cos(u) du = u*sin(u) -int sin(u) du = usin(u) -(-cos(u)) +C = usin(u) + cos(u)+C Plug-in u = x^2 on usin(u) + cos(u)+C , we get the complete indefinite integral as: int 2x^3 cos(x^2) dx =x^2sin(x^2) +cos(x^2) +C