Question

What is a "normal line"? they say to get the normal line of a parabola...

Answer 1

A parabola goes into a curve..is that what they mean?

Answer 2

I know that, I need to know what a "normal line" is

Answer 3

Shouldn't there be an equation with that?

Answer 4

Hold on that was a stupid question..and I know the answer to this...Gimme a minute.

Answer 5

they say "Find the equation of the normal line to the parabola y=x^2 - 5x +4 that is parallel to the line y= (1/3)x -5/3

Answer 6

http://answers.yahoo.com/question/index?qid=20071125140023AAebnO1 You mean this?

Answer 7

I read that, but it made no sense to me

Answer 8

Oh..okay. Well I can't find anything else. Sorry. Hope you get help Dooooom.

Answer 9

ok

Answer 10

perpendicular to tangent line

Answer 11

but the tangent line can be allot of places

Answer 12

....?

Answer 13

it can be at most; in 2 places ...

Answer 14

what is the perp slope of the parallel line?

Answer 15

1/3

Answer 16

thats the line that the normal is parallel to; we want a tangent, not a normal; so perp that slope; flip and negate

Answer 17

-3?

Answer 18

good

now find the derivative of the ellipse equation that gives us a value of -3

Answer 19

The normal line is the line perpendicular to the slope of the curve at the point of intersection. The normal is therefore perpendicular to the tangent line

Answer 20

or equate it to the line: y=-3x+c ; and retrive 2 solutions for c

Answer 21

@ZhangYan where it intersects what?

Answer 22

but id go my first idea; find the points then establish the lines

Answer 23

so, i need to find the derivative of the parabola, right?

Answer 24

the equation you provided yes; I thought you said it was an ellipse :)

Answer 25

it is a parabola

Answer 26

f' = -3 is what you want to solve

Answer 27

how though?

Answer 28

sorry if i am asking stupid questions, my mind is just going blank

Answer 29

if you havent taken calculus yet, then derivatives wont make sense to you

Answer 30

if you have taken calculus, then this is the simplest of derivatives .... its a power rule

Answer 31

i am taking it right now, i am just really struggling with it

Answer 32

i am in chapter 3

Answer 33

\[\frac{d}{dx}x^n=nx^{n-1}\]

Answer 34

i know how to get derivatives with the formulas they give you

Answer 35

so, once you get -3, what do you do next?

Answer 36

the x value for f'=-3 is the x value you need to use in y to find the value if y so that you have a point to create the parallel line with.

the slope of the parallel is the slope of the given: 1/3

you have a point to attach it to, so use the point slope form of a line to determine the outcome

Answer 37

i should used consistent letters ....

the x value for y' = -3 is the same x value to use in the y= part

Answer 38

ok, i think i get it now...

Answer 39

good luck ;)

Answer 40

thank you for your help