var('x,y,z,t')
f(x,y,z)=4*x*y/((x^2+1)*(y^2+1))-z
fx(x,y,z)=diff(f,x)
fy(x,y,z)=diff(f,y)
fz(x,y,z)=diff(f,z)
print "x=",(fx(1,1,1)*t+1)
print "y=",(fy(1,1,1)*t+1)
print "z=",(fz(1,1,1)*t+1)
a=parametric_plot3d([fx(1,1,1)*t+1,fy(1,1,1)*t+1,fz(1,1,1)*t+1],(t,0,1))
a