Se considera functiile f.F : R=>R date prin 
f(x)=[tex] e^{x} + 3 x^{2} + 2 si F(x) = e^{x}+ x^{3} +2x-1 [/tex]

c) Sa se demonstreze ca [tex] \int\limits^1_0 {(xf(x)+F(x)} \, dx = F(1)[/tex]

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Răspuns :

Se observă că [tex]F'(x)=f(x)[/tex].
Atunci [tex]\displaystyle\int_0^1\left[xf(x)+F(x)\right]dx=\int_0^1\left[xF'(x)+x'F(x)\right]dx=\\=\displaystyle\int_0^1\left[x\cdot F(x)\right]'dx=\left. x\cdot F(x)\right|_0^1=F(1)[/tex]