Question 1125618
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Any line parallel to y = -x+7 will have a slope of <b><font size=4>-1</font></b>.
Any line perpendicular to y = -x+7 will have a slope of <b><font size=4>1</font></b>.
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Recall that y = mx+b gives us the slope to be m. Since y = -x+7 is in this form, we see that m = -1 is the slope of this line. Anything parallel to it will also have an equal slope (of -1)


Think of -1 as -1/1. We can flip the fraction and flip the sign to get +1/1 or just 1 as the perpendicular slope. Note how multiplying the original slope (-1) and the perpendicular slope (-1) leads to a result of -1. 


The general rule is that m*n = -1 where
m = original slope
n = perpendicular slope
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