\frac d{dx}\left(\left(\frac{dA}{dx}+jKA\right)\exp(jKx)\right)=\left(\frac{d^2A}{dx^2}+jK\frac{dA}{dx}\right)\exp(jKx)+\left(\frac{dA}{dx}+jKA\right)\exp(jKx)jK=\left(\frac{d^2A}{dx^2}+2jK\frac{dA}{dx}-K^2A\right)\exp(jKx)