Tính tích phân sau
\[\int \limits^\frac{1+\sqrt{5}}{2}_0 \dfrac{\left(x^2+1\right)\mathrm{d} x}{x^4-x^2+1}\]
Chú ý rằng: $\frac{x^2+1}{x^4-x^2+1}=\frac{1}{2(x^2+x\sqrt{3}+1)}+\frac{1}{2(x^2-x\sqrt{3}+1)}=\frac{1}{2(x+\frac{\sqrt{3}}{2})^2+\frac{1}{2}}+\frac{1}{2(x-\frac{\sqrt{3}}{2})^2+\frac{1}{2}}$
$\implies \int \frac{(x^2+1)dx}{x^4-x^2+1}=\frac{1}{2}\int \frac{dx}{(x+\frac{\sqrt{3}}{2})^2+\frac{1}{4}}+\frac{1}{2}\int \frac{dx}{(x-\frac{\sqrt{3}}{2})^2+\frac{1}{4}}$
Tới đây đặt $u=x+\frac{\sqrt{3}}{2}\implies du=dx\implies \int \frac{dx}{(x+\frac{\sqrt{3}}{2})^2+\frac{1}{4}}=2\int \frac{2du}{4u^2+1}=2\arctan(2u)=2\arctan(2x+\sqrt{3})$
Tương tự, ta tìm được $\int \frac{(x^2+1)dx}{x^4-x^2+1}=\arctan(2x+\sqrt{3})+\arctan(2x-\sqrt{3})$