URGENT! y=x^3+2x^2-x -1

[kantev]

How do i solve the function y=x^3+2x^2-x -1 in the interval [1/2;2].
Graph the function in MS Excel in the interval [1/2;1].

 

[Deleted member 4993]

How do i solve the function y=x^3+2x^2-x -1 in the interval [1/2;2].
Graph the function in MS Excel in the interval [1/2;1].

What method/s have you been taught to calculate roots of rational polynomials?

 

[Dr.Peterson]

How do i solve the function y=x^3+2x^2-x -1 in the interval [1/2;2].
Graph the function in MS Excel in the interval [1/2;1].

What do you mean by "solve the function"? Do you just mean to find the zero of the function in that interval, or to find the inverse of the function with that restricted domain (that is, solve for x in terms of y)?

This function has no rational zeroes, so you can probably only find an approximation to the one you are asked for (unless you use very complicated work to get an exact value).

Please state the exact wording of the problem you were given. I would guess that you have learned some methods of approximation, or else are to estimate the solution from the graph. But unless you tell us, we can't know what is expected.

 

[mmm4444bot]

URGENT!

I hope there's no emergency! We don't have any paid staff on call.

… y = x^3 + 2x^2 - x - 1 in the interval [1/2;2] …

… MS Excel [graph] in the interval [1/2;1]

Are these two intervals supposed to be the same?

By the way, standard interval notation uses a comma, not a semi-colon.

If you're trying to find the x-intercept (the polynomial's root) within the interval [1/2, 1] and your class uses Excel then you could use Excel's built-in feature called GOAL SEEK described with an example here (Copyright 2015 Kardi Teknomo).

Alternatively, you could graph the equation first, and then use Excel's zooming tools to read off a decimal approximation.

If you're looking for something else, you'll need to be more specific. :cool:

 

[kantev]

I have to calculate the zero of the function to the third digit, i should either use the lagrange interpolation or the regula falsi method , i am not sure ( But some help would be very much appreciated

 

[mmm4444bot]

I have to calculate the zero of the function to the third digit, i should either use the lagrange interpolation or the regula falsi method , i am not sure (But some help would be very much appreciated)

It's still not clear what kind of help you need.

Do you need help coding the algorithm, using Excel?

Or, do you need help understanding the explanation of the regula falsi method that you were given?

Where are you stuck exactly?

If I needed to program Excel to estimate the zero, using the regula falsi method, then I would begin by googling keywords like:

regula falsi method

or

false-position method using Excel