a = 0.8
kette(x) = (a * cosh(x / a))
f: x = 2
g: x = -2
y_A: (a * cosh(2 / a))
A: (-2, y_A)
B: (2, y_A)
bq: (4 * a^(2) / (y_A^(2) - a^(2)))
hyp: ((-a^(2)) * x^(2)) + (bq * y^(2)) = (a^(2) * bq)
b: sqrt(bq)
d: (y_A - a) / 4
para(x) = (d * x^(2)) + a
c: (y_A - a) / 16
poly4(x) = (c * x^(4)) + a