f_1(x) = (5 * x) - 2 - ((25 * x^(2)) - (9 * x) + 8)^(1 / 2)
f_2(x) = (2 * x) + 9 - ((4 * x^(2)) + (13 * x) - 5)^(1 / 2)
f_4(x) = tan(x - 2) / (x^(6) - (5 * x^(5)) + (6 * x^(4)))
f_3(x) = (x^(5) - (7 * x^(4)) + (12 * x^(3))) / tan(x - 4)
f_5(x) = ((x - 7) / (x + 3))^(x - 2)
f_6(x) = ((x + 8) / (x - 5))^(x - 3)