Prove that $\cos\left(2x\right)=0$ is not an identity

Compute the integral

$\int xdx$

Compute the integral

$\int\left(x\cdot\cos\left(2x^2+3\right)\right)dx$

Compute the integral

$\int x\left(x^2-3\right)dx$

Compute the integral

$\int x^2\sin\left(x\right)dx$

Compute the integral

$\int x^2\cos\left(2x\right)dx$

Compute the integral

$\int x^2\ln\left(x\right)dx$

$\frac{d}{dx}\left(2x+1\right)$