# Find k such that the line is tangent to the graph

1. May 20, 2004

### kdinser

I'm not sure what they are looking for here.

Find k such that the line is tangent to the graph of the funtion

Function: x^2-kx Line: 4x-9

Just need a little push in the right direction.

2. May 20, 2004

### arildno

Hints:
You must find 2 features:
a) A point in common between the graphs of your function and your line.
b) That the slope of the function at that point equals the line's slope

This is a system of two equations!
Solutions to this system is what you are looking after (a k-value will be one of the numbers in a given solution, a x-value of the point of intersection will be the other number)

3. May 20, 2004

### kdinser

thanks, I'll give it a shot.

4. May 20, 2004

### Muzza

A solution that doesn't involve calculus: if the line is supposed to tangent the other function, then the equation 4x - 9 = x^2 - kx may only have one solution. If you solve this for x, what can you say about the discriminant?

5. May 20, 2004

### Muzza

arildno, did you see your mistake (in the deleted post), or did you remove it in order to not rouse my anger?

6. May 20, 2004

### arildno

That's why I deleted my dumb message..