已知x_1、x_2、p、q，且x_n=p*x_{n-1}+q*x_{n-2}，x_n的通项公式

x_n=-(sqrt(4*q+p^2)*((p*(sqrt(4*q+p^2)+p)^n-p*(p-sqrt(4*q+p^2))^n)*x2+(((-2*q)-p^2)*(sqrt(4*q+p^2)+p)^n+(2*q+p^2)*(p-sqrt(4*q+p^2))^n)*x1)+(((-4*q)-p^2)*(sqrt(4*q+p^2)+p)^n+((-4*q)-p^2)*(p-sqrt(4*q+p^2))^n)*x2+((4*p*q+p^3)*(sqrt(4*q+p^2)+p)^n+(4*p*q+p^3)*(p-sqrt(4*q+p^2))^n)*x1)/(2^(n+3)*q^2+2^(n+1)*p^2*q)