ecuació diferencial series

y(x) = ∑ ( k!·x^{(k+1)} )


x^{2}·d_{x}[y(x)] = y(x)


x^{2}·d_{x}[ ∑ ( k!·x^{(k+1)} ) ] = ∑ ( (k+1)!·x^{(k+2)} )


p = k+1 <==> p+1 = k+2


∑ ( (k+1)!·x^{(k+2)} ) = ∑ ( p!·x^{(p+1)} )