f(x)= \sqrt{ x-a } 

f(x) = 1.0 / sqrt(x)
g(x) = 1.0 / sqrt(x - 1.0)
h(x) = 1.0 / sqrt(x - 3.0)
a = -1.1 (slider from -5 to 5, step 0.1)
p(x) = 1.0 / sqrt(x - a)