show
x cubed + 4x =1 has a solution between x = 0 and x = 1
It has 3 roots, one "real" and two "complex":
1 - x≈ 0.24627
2 - x≈ -0.1231 - 2.0113 i
3 - x≈ -0.1231 + 2.0113 i