I am trying to prove the expression for Dickson polynomials:
$$D_n(x, a)=\sum_{i=0}^{\lfloor \frac{n}{2}\rfloor}d_{n,i}x^{n-2i}, \quad \text{where} \quad d_{n,i}=\frac{n}{n-i}{n-i\choose i}(-a)^i$$
I am supposed to use the recurrence relation:
$$D_n(x,a)=xD_{n-1}(x,a)-aD_{n-2}(x,a)$$
I have...