You can transform your equation d2y/dx2=.-5dy/dx-7y to get:
y1=y
y2=dy/dx
dy1=dy/dx=y2
dy2=d2y/d2x=-5dy/dx-7y=-5y2-7y1
Create a file named myode.m
function dy=myode(x,y)
dy=[0;0]
dy(1)=y(2)
dy(2)=-5*y(2)-7*y(1)
Then run these lines
yin=[0 4 ] % initial values
time=[0 5]
[x,y]=ode45(@myode,time,yin)
plot(x,y)
