Applicare la formula: $\int\frac{e^x}{x}dx$$=Ei\left(x\right)+C$, dove $int2.718281828459045^x/x$dx=\int\frac{e^u}{u}du$, $2.718281828459045=e$, $dx=du$, $int2.718281828459045^x/x=\int\frac{e^u}{u}$, $x=u$, $2.718281828459045^x=e^u$ e $2.718281828459045^x/x=\frac{e^u}{u}$

Applicare la formula: $\left[x\right]_{a}^{b}$$=eval\left(x,b\right)-eval\left(x,a\right)+C$, dove $a=y$, $b=x$ e $x=Ei\left(u\right)$