Math Is Fun Forum

butterscotchlover2

Member

Registered: 2017-06-15

Posts: 2

Graphing Functions

A portion of the graph of f(x)=ax^3+bx^2+cx+d is shown below.

What is the value of 8a-4b+2c-d?

Graph

To view the graph properly, right click the image and click open image in a new tab.

Thanks

Bob

Administrator

Registered: 2010-06-20

Posts: 10,134

Re: Graphing Functions

Hi butterscotchlover2

Welcome to the forum.

Hard to tell from the image I am viewing but it looks like the curve crosses the x axis at 0 1 & 2

That would make the function ax(x-1)(x-2)

Also looks like (4,3) is on the curve which will tell you the value of a.

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

butterscotchlover2

Member

Registered: 2017-06-15

Posts: 2

Re: Graphing Functions

I am confused, how does (4,3) tell me the value of a.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,134

Re: Graphing Functions

There are 4 unknowns so, normally, you would need 4 bits of information.  The 3 crossing points isn't enough so I looked for a point on the graph.  If you put x=4 & y=3 you be able to rearrange to find a.  If you then expand the brackets you will be able to find all the unknowns.

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

stelii123

Member

Registered: 2017-06-27

Posts: 1

Re: Graphing Functions

4x2 – 4x + 1 = 0