β {\displaystyle \beta } ) ogni frazione semplice del tipo
A x + a {\displaystyle {\frac {A}{x+a}}} ;
β ′ {\displaystyle \beta '} ) ogni frazione semplice del tipo
M x + N x 2 + p x + q {\displaystyle {\frac {Mx+N}{x^{2}+px+q}}} ( p 2 4 − q < 0 ) {\displaystyle \left({\frac {p^{2}}{4}}-q<0\right)} ;
γ {\displaystyle \gamma } ) ogni espressione d d x V x W ( x ) {\displaystyle {\frac {d}{dx}}{\frac {Vx}{W(x)}}} .
Ora gli integrali di ( α ) {\displaystyle (\alpha )} , ( β ) {\displaystyle (\beta )} , ( γ ) {\displaystyle (\gamma )} sono rispettivamente
k 0 x + k 1 x 2 2 + k 2 x 3 3 + . . . . . + k s x s + 1 s − 1 + cost {\displaystyle k_{0}x+k_{1}{\frac {x^{2}}{2}}+k_{2}{\frac {x^{3}}{3}}+.....+k_{s}{\frac {x^{s+1}}{s-1}}+{\text{cost}}} .
A log | x + a | + cost {\displaystyle A\log |x+a|+{\text{cost}}} .
V ( x ) W ( x ) + cost {\displaystyle {\frac {V(x)}{W(x)}}+{\text{cost}}} .
Basterà saper calcolare l'integrale di β ′ {\displaystyle \beta '} ), cioè:
∫ M x + N x 2 + p x + q d x {\displaystyle \int \,{\frac {Mx+N}{x^{2}+px+q}}dx} ( p 2 4 − q < 0 cioe k = q − p 2 4 reale ) {\displaystyle {\frac {p^{2}}{4}}-q<0 \choose {\text{cioe}}\,k={\sqrt {q-{\frac {p^{2}}{4}}{\text{reale}}}}} .
Ora:
M x + N = M 2 ( 2 x + p ) + ( ( N − p M 2 ) {\displaystyle Mx+N={\frac {M}{2}}(2x+p)+(\left(N-p{\frac {M}{2}}\right)} .
Cosicchè: ∫ M x + N x 2 + p x + q d x = M 2 ∫ 2 x + p x + p x + q d x + ( N − p M 2 ) ∫ d x x 2 + p x + q {\displaystyle \int {\frac {Mx+N}{x^{2}+px+q}}dx={\frac {M}{2}}\int {\frac {2x+p}{x^{+}px+q}}dx+\left(N-p{\frac {M}{2}}\right)\int {\frac {dx}{x^{2}+px+q}}} Ora:
∫ 2 x + p x 2 + p x + q d x = log ( x 2 + p x + q ) {\displaystyle \int {\frac {2x+p}{x^{2}+px+q}}dx=\log(x^{2}+px+q)} .
E, poichè
x 2 + p x + q = ( x + p 2 ) 2 + k 2 {\displaystyle x^{2}+px+q=\left(x+{\frac {p}{2}}\right)^{2}+k^{2}} ,
sarà:
∫ d x x 2 + p x + q = ∫ d ( x + p 2 ) ( x + p 2 ) − 2 + k 2 = 1 k artg x + p 2 k {\displaystyle \int {\frac {dx}{x^{2}+px+q}}=\int {\frac {d\left(x+{\frac {p}{2}}\right)}{\left(x+{\frac {p}{2}}\right)^{-2}+k^{2}}}={\frac {1}{k}}\,{\text{artg}}\,{\frac {x+{\frac {p}{2}}}{k}}} .