set xrange [-6:6]
set yrange [-1:5]
set zeroaxis
set nokey
set label '\small{$[x_0,f(x_0)]$}' at 7/4, 3/2
f(x)=(x<-5)? sqrt(x):(x<=4) ? sqrt(4-x) : sqrt(-1)
plot f(x),(4-x)/3,(25-4*x)/12