=ye^(x/y)丨(y^2,0)=y(e^y-1)
=3e^(x/3)=3(e^3-1)
∫[0：y²]e^(x/y)dx=y∫[0：y²]e^(x/y)d(x/y)=y·e^(x/y)|[0：y²]=y·[e^(y²/y)-e^(0/y)]=y·(eʸ-1)
