Riemann Simulation

$f\left(x\right)=$

$f\left(x\right)=x$ $f\left(x\right)=x^2$ $f\left(x\right)=x^3$ $f\left(x\right)=\sin \left(x\right)$ $f\left(x\right)=\cos \left(x\right)$ $f\left(x\right)=\tan \left(x\right)$