*y*= (

*x*-1)(

*x*+4)?

I spend way too much of my time doing stuff like this. I write and rewrite questions and then send them off with poorly drawn graphs and hope someone with actual ability with computerized graphics can make it look like it should. I send these types of jpgs at least a couple of times a week and every time I do it, I think how much easier it would be to have a fucking scanner. So, I make my (poor attempt at a) drawing, take a picture of it with our digital camera, email it to myself, open it up in Picasa, do whatever I have to do to make it legible, save it to my computer, and then I put it in an email to whoever needs the email. And then I laugh to myself and say it's better than faxing. Which is true, but I live in 2012!! Okay, I'm over it.

Plus, as part of the technology deal at his new school, my husband is getting a scanner. Thank whatever deity you wish to thank!!

**EDITED TO ADD**: Because Elizabeth wanted the answer, here it goes.

So if you have

*y*= (

*x*-1)(

*x*+4), the zeroes, where the graph crosses the

*x*-axis, are located where the

*y*-value is zero. Any point on the

*x*-axis will be in the form of (

*x*, 0). So all you need to do is set the equation equal to zero, which is to say, make

*y*= 0.

0 = (

*x*-1)(

*x*+4)

You may remember from third grade the zero product property (ha ha - maybe not). If you have

*ab*= 0, either

*a*must be 0 or

*b*must be zero because if the product is 0, one of the terms must be zero. If we apply that rule to our equation, then either

*x*- 1 = 0 OR

*x*+ 4 = 0

Now we solve those with our rusty algebra skillz. If

*x*- 1 = 0, that makes

*x*= 1. If

*x*+ 4 = 0, that makes

*x*= -4.

So we know our graph must cross at (1, 0) and (-4, 0). We can eliminate C & D because the test makers are attempting to confuse us with the wrong signs. Since parabolas, this type of graph, usually open up, unless it is multiplied by a negative number, we know this one must point up. For example, -1(

*x*-1)(

*x*+4) would be B because the -1 in front would flip the parabola over. Cross off B. The answer is A.

I want to know the answer!

ReplyDeleteI almost failed grade 12 math. And that was with 2 hours of tutoring a week!

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