Classify the fixed points at the origin and sketch an accurate phase portrait (based on the eigendirections) for each of these systems:
$$(i) \frac{dx}{dt}=36x-16y, \frac{dy}{dt}=-3x+28y$$ $$(ii) \frac{dx}{dt}=-31x+y, \frac{dy}{dt}=9x-39y$$
Completely stuck on this one, any help appreciated