Resolução pelo dicotomia de uma função f(x) = x**2 + x - 20. 

0, 0, 5, 2.5, 2.5
1, 2.5, 5, 3.75, 1.25],
2, 3.75, 5, 4.375, 0.625
3, 3.75, 4.375, 4.0625, 0.3125
4, 3.75, 4.0625, 3.90625, 0.15625
5, 3.90625, 4.0625, 3.984375, 0.078125
6, 3.984375, 4.0625, 4.0234375, 0.0390625
7, 3.984375, 4.0234375, 4.00390625, 0.01953125
8, 3.984375, 4.00390625, 3.994140625, 0.009765625
9, 3.994140625, 4.00390625, 3.9990234375, 0.0048828125
10, 3.9990234375, 4.00390625, 4.00146484375, 0.00244140625
11, 3.9990234375, 4.00146484375, 4.000244140625, 0.001220703125
12, 3.9990234375, 4.000244140625, 3.9996337890625, 0.0006103515625