4/19/10

Test 7 Section 9 - #11 (page 798)

You can use your graphing calculator to help you visualize this (if you use a graphing calculator).  They tell you the slope of the line is -4/5, so you can graph a line with that slope simply by putting "y = (-4/5)x" in your calculator.  You can do the same with all the answer choices, and eyeball pretty easily which one is a true reflection across the x-axis.

Let's assume for a minute that you're doing this question without a graphing calculator, though.  A reflection across the x-axis negates the y-values of your graph.  How will that affect the slope?  Well, let's use the same equation I made up above to see:

2 easy points to find on that graph are (0,0), and (5,-4). If I reflect those two points across the x-axis, what happens?  (0,0) stays the same.  (5,-4) reflects to (5,4), because we're negating the -4, to get +4.  What's the slope of a line that goes through (0,0) and (5,4)?



(B) is our answer.

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