A = (-0.24, 3.94)
r = 1.8 (slider from 1 to 5, step 0.1)
c = Circle(A, r)
B = Point(c)
z: π * r^(2)
f: z / r^(2)
texto3: "A = área\ do\ círculo = π r^2= \pi\ (" + (LaTeX[r]) + ")^2= " + (LaTeX[z]) + ""