Need help with TI-83 plus calculator

[Hot Lava Mama]

When graphing inequalites such as "less than or equal to", is there a different way to graph "less than" compared to "less than or equal to"? We understand that if he were drawing it by hand, the one that has the "equal to" should be a solid line and include all points on that line, and that the one without the "equal to" should be a dotted line and points on that line are NOT included. However, we can't seem to figure out if there is a different way to put these into the calculator. Is he just suppose to "know" from the equation that it should be either solid or dotted? Not a big deal, just wondering how to do it. We know how to graph without the "equal to", can figure out how to include the "equal to".

 

Does this make sense?

 

Hot Lava Mama

[Hot Lava Mama]

:bigear:

[Dana]

Is he just suppose to "know" from the equation that it should be either solid or dotted? Not a big deal, just wondering how to do it. We know how to graph without the "equal to", can figure out how to include the "equal to".

 

 

I guess I'm not understanding your question.

 

Yes... one should know from the equation whether the line should be solid or dotted.

Solid if equality is there (less than or equal; greater than or equal); dotted if we have a strict inequality (< or >).

 

When graphing by hand, you'd first graph the line as solid or dotted as the boundary, then use a test point to determine shading (the true part of the inequality). That's the fastest and typically easiest way to graph inequalities in 2 variables by hand.

 

When using the calculator, you have to solve the inequality for y. BE CAREFUL to remember that if you multiply or divide by a negative number, you must reverse the inequality.

 

So, if you were graphing 3x - 2y < 6, solving for y, you get

-2y < -3x + 6

y > 3/2 x - 3

 

On the calculator, go to y= menu and type y1 = (3/2) x - 3

Then you can move the cursor to the left of y1 where you can see the line...

Here, y is GREATER than the line we've graphed, so we want to shade ABOVE the line.

Click enter until shading above the line shows up.

Then when you graph, you'll have the shading done.

You do need to know that the line is NOT included though.

 

There may be programs out there that would graph and show the line as dotted, but I don't see the need.

 

HTH.

[Hot Lava Mama]

 

 

You do need to know that the line is NOT included though.

 

There may be programs out there that would graph and show the line as dotted, but I don't see the need.

 

HTH.

 

Thanks so much for your help. He does know how to graph them by hand (dotted versus solid line) and we also figured out how to do the inequality (less than or greater than) on the calculator. The thing we couldn't figure out was if there was a different way we needed to do it if it included the "or equal to" in the inequality.

 

I originally said to ds that he would know if the line should be included or not by looking at the problem. I wasn't sure if it was a big deal because I have never used a graphing calculator, so ds and I are learning together. I didn't want to just ignore it in case it was important later on. That's why I came here to find out if there was a secret way to do it that we would need later on.

 

So, from what I gather from your information, we are doing everything we need to. He can make the shading part correctly (he goes over to the side where there is a blinking light and he get the shading triangle on the top or bottom) then he just has to know whether the numbers on the line is included based on the formula he is graphing. Nothing different needs to be done for "less than" versus "less than or equal to". Do I understand this correctly?

Thanks so much for your help! I appreciate your time.

Hot Lava Mama

[Dana]

I do not know of a way on the TI to show whether the inequality is included or not when graphing. There may be programs for it that would.

 

Personally, my preference is to do the work by hand. :)

[Hot Lava Mama]

Thanks Dana!

:)