y=0 is a horizontal null cline and x=0 is a vertical nullcline. What are the other two nullclines?
Wouldn't they just be (just set the derivative to zero?):
for the v nullcine for the h nullcline
No, a nullcline is a line not a parabola. dx/dt= 0 when y(4- 2x-y)= 0. That will clearly happen when the factor y= 0 which is why they said that "y= 0 is a horizontal nullcline". What is the other factor?