1:  f(2.5) = 0
2:  After 5 add_term calls:  f(x) = -1 x^5 + 5 x^3 - 1 x + 2
3:  f1(x) = 1 x^2 - 1
4:  f2(x) = 1 x^2 + 1
5:  f1+f2 = 2 x^2
6:  f1-f2 = -2
7:  f1*f2 = 1 x^4 - 1
8:  f1(x) = -8 x^7 + 2 x^5 + 3 x^4 + 1 x^2 - 1
9:  f1(2.0) = -909
10: f2(x) = 3 x^8 + 1 x^6 + 2 x^5 - 3 x^4 + 1 x^2 + 1
11: f1+f2 = 3 x^8 - 8 x^7 + 1 x^6 + 4 x^5 + 2 x^2
12: f1-f2 = -3 x^8 - 8 x^7 - 1 x^6 + 6 x^4 - 2
13: f1*f2 = -24 x^15 - 2 x^13 - 7 x^12 + 26 x^11 + 10 x^10 - 8 x^9 - 11 x^8 - 4 x^7 - 1 x^6 + 7 x^4 - 1