#1.5 FE3
shark_tuna_vector(t,s)= (0.5*t-0.01*s*t, 0.005*s*t-0.2*s)
p=plot_vector_field(shark_tuna_vector,(t,0,100),(s,0,100), axes_labels=["Tuna", "Shark"])
show(p)

spring_friction_vector(x,v)= (v,-x-v)
p=plot_vector_field(spring_friction_vector,(x,-10,10),(v,-10,10), axes_labels=["X", "V"])
show(p)