Numerically solve for x in a polynomial equation

If I have a 3rd order polynomial (y = ax^3 + bx^2 + cx + d) with all the coefficients known, how do I plug in a y number and get out the x number?

Answer 1

[Honglei Chen]

Write the polynomial as

a*x^3+b*x^2+c*x+d-y

Then you can use fzero to solve x.

doc fzero

[Brian Haab]

Great - thank you.

Answer 2

[Walter Roberson]

roots( [a, b, c, d-y] )

[Brian Haab]

Thanks also for this answer.