Solve the equation for 0 and 1:
x^3 + 6x -5
Replace x with 0:
0^3 + 6(0) -5 = -5
Replace x with 1:
1^3 + 6(1) -5 = 1+6 -5 = 2
Because the value of f(0) is negative and the value of f(1) is positive then there is at least one value of x between 0 and 1 that f(x) = 0