# 5 a)

> ode1 := diff( x(t), t ) = 10*(y(t)-x(t)) :

> ode2 := diff( y(t), t ) = 28*x(t)-y(t):

> ode3 := diff( z(t), t ) = -8/3*z(t):

> MODELa := [ ode1, ode2 ] ;

> MODELb := [ ode3 ] ;

> VARa := { x(t), y(t) } ;

Direction Field, Phase Portrait, and Solution Curves ( DEplot3d )