The question was: Which best represents the graph of 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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