Left Riemann sum for tan(x) on [0,1] with n=5

Since $a=0$, $b=1$, and $n=5$, the width of each subinterval is $\Delta x = \frac{1-0}{5} = 0.2$. The subinterval endpoints are $x_0=0, x_1=0.2, x_2=0.4, x_3=0.6, x_4=0.8, x_5=1$. For a left sum we use the left endpoints of each subinterval: $x_0, x_1, x_2, x_3, x_4$, i.e. $0, 0.2, 0.4, 0.6, 0.8$.

Evaluating $f(x)=\tan(x)$ at these points gives approximately $\tan(0)=0$, $\tan(0.2)\approx 0.2027$, $\tan(0.4)\approx 0.4228$, $\tan(0.6)\approx 0.6841$, $\tan(0.8)\approx 1.0296$. Summing these values gives approximately $2.3392$, and multiplying by $\Delta x = 0.2$ gives the left Riemann sum $\approx 0.4678$.