Expert: Paul Klarreich - 11/26/2008

Question
QUESTION: y=|x|+3

I had to graph this equation. I used the pairs(4,7); (2,5); (1,3). My line was not straight. Any reason for this? Negatives don't work for x either.

ANSWER: Questioner:   Karima
Category:  Advanced Math
Private:  No
 
Subject:  graphing equations
Question:  y=|x|+3

I had to graph this equation. I used the pairs(4,7); (2,5); (1,3). My line was not straight. Any reason for this? Negatives don't work for x either.
.................................
Hi, Karima,

Most of the problems that students have in mathematics come down to one thing:

YOU MUST USE VOCABULARY CORRECTLY.

A 'line' is always straight -- there is no such thing as a 'line that was not straight.'   

But the graph does not have to be a line; it can be something else.

Now the first step in graphing:

y=|x|+3

is READING IT.  If you don't know what it says, and I mean COMPLETELY what it says, you can't do anything with it.

So that is your starting point:

Write out y=|x|+3  in words.  Then make sure you know what the words themselves mean.  Send along what you have and we'll go from there.


---------- FOLLOW-UP ----------

QUESTION: here is the what I worked out. I used different ordered pairs plus a negative to show my graph. Does this make sense now?

Answer
Questioner:   Karima
Category:  Advanced Math
Private:  No
 
Subject:  graphing equations
Question:  y=|x|+3

I had to graph this equation. I used the pairs(4,7); (2,5); (1,3). My line was not straight. Any reason for this? Negatives don't work for x either.
.................................
Hi, Karima,

Most of the problems that students have in mathematics come down to one thing:

YOU MUST USE VOCABULARY CORRECTLY.

A 'line' is always straight -- there is no such thing as a 'line that was not straight.'   

But the graph does not have to be a line; it can be something else.

The first step in graphing:

y=|x|+3

is READING IT.  If you don't know what it says, and I mean COMPLETELY what it says, you can't do anything with it.

So that is your starting point:

Write out y=|x|+3  in words.  Then make sure you know what the words themselves mean.  Send along what you have and we'll go from there.


---------- FOLLOW-UP ----------

QUESTION: here is the what I worked out. I used different ordered pairs plus a negative to show my graph. Does this make sense now?

...........................................

HI again,

It's making more sense now --hopefully TO YOU.  But your graph is no good -- it's time you realized that the number of points needed to get a good graph varies with the type:

y = constant;  One.
y = linear function:  Two
y = anything else: HUMONGOUS number of points.

So a couple of new points "plus a negative" does not cut it.  You either have to;

A. Plot about 20-50 points.
B. Analyze and understand the function so you know WHICH points to plot.

Guess which you are supposed to be doing in a math class.


You didn't do what I asked: Write out the definition of your function in words.  I expected you to write:

The function says: "y is equal to 3 more than the absolute value of x"

and

"the absolute value of x is x-itself if x is positive or zero, and the opposite of x if x is negative"

Also, you have to send along a statement of EXACTLY what you are studying in math, so I know what NOT to tell you.

Your graph should look like the picture I am sending you.