# Homework Help: Finding Constants given certain constraints.

1. Feb 24, 2010

### Econometricia

1.Find a such that y=x2 - 2(x)1/2 + 1 is perpendicular to ay + 2x =2 when x=4

3.I have gotten as far as getting the slope of the normal line. I then rearranged the equation to y = (-2x+2)/ (a) and That is where I am stuck

I am having a lot of trouble with these types of questions. =(

2. Feb 24, 2010

### Staff: Mentor

Does that mean you have found the slope of the line? What normal line are you talking about? You need the derivative of the curve. That's not what you were talking about, is it?

3. Feb 24, 2010

### Econometricia

The slope of the normal line as in the inverse slope of the tangent line at x=4. So y' |x=4 = 15/2 = mtan , so Mnormal= -2/15

4. Feb 24, 2010

### Staff: Mentor

OK, so you know the slope of the line ay + 2x = 2 has to be -2/15 when x = 4. It looks like you've already done all the hard work; the rest is easy.

5. Feb 24, 2010

### Econometricia

I know the slope has to be(-2/15) and that y= -2x/a + 2/a What to do from here is really just not clicking.

6. Feb 24, 2010

### Staff: Mentor

Given this line -- y= -2x/a + 2/a -- what is an expression that represents its slope?

7. Feb 24, 2010

### Econometricia

I am sorry. I just cant figure out how to get the a. Just one of those nights. =P I guess I will try and figure out in the morning before the test =). Thank You for your help Mark.

8. Feb 24, 2010

### Staff: Mentor

I wasn't asking for a, just an expression that represents the slope of the line y = (-2/a)x + 2/a.