Math Is Fun Forum

SmellyMan

Member

Registered: 2011-03-06

Posts: 63

I have no idea how this is called in english. Sorry.

So I have a function: f(x)=nx^2+2x+n

And I have to put n like that so the function TOUCHES the x axis.

So I went on with this formula:

D=b^2-4ac

And if it touches that means that D=0.

0=4-4(n)(n)
0=4-4n^2

I am completely stumped here on what to do next.

4(1-n^2)=0

I tried this and the result is 1. But there was supposed to be 2 solutions to this problem ^.^. Any help greatly appriciated! Thank you.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,157

Re: I have no idea how this is called in english. Sorry.

hi Smellyman,

What you have done is good.

So two things are multiplied and the product is zero => one of the things must be zero.

As it isn't the 4 it must be the other

There's the two solutions.

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

SmellyMan

Member

Registered: 2011-03-06

Posts: 63

Re: I have no idea how this is called in english. Sorry.

How did I miss -1. Argh, silly me ^^. Thank you, kind sir! (:

Bob

Administrator

Registered: 2010-06-20

Posts: 10,157

Re: I have no idea how this is called in english. Sorry.

hi

You're welcome.  Don't worry about missing that;  it happens to us all at some time. 

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