Perpendicular lines, equal aspect

apple2357

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Mar 9, 2018
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Something i had never fully appreciated, until recently is when you talk about two lines being perpendicular the scales are automatically assumed to be equal aspect , otherwise the lines do not 'look' perpendicular? Is this always clear to students? Otherwise you get some odd looking results?

12561

Is y=2x perpendicular to y= -0.5x ? Or only when the scales are equal aspect?
 

MarkFL

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Two lines in the plane are perpendicular when the product of their slopes is -1. In order for them to look perpendicular when graphed, yes, the two axes must be equally scaled.
 

Dr.Peterson

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Nov 12, 2017
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To put it another way, when we talk about perpendicular lines on a coordinate plane (or about angles in general), we are assuming that the axes have the same scale.
 

apple2357

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Mar 9, 2018
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yes, it appears so. Not something i had ever thought about before!
 

lookagain

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Aug 22, 2010
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Two lines in the plane are perpendicular when the product of their slopes is -1. In order for them to look perpendicular when graphed, yes, the two axes must be equally scaled.
Also, two lines in the plane are perpendicular if the slope of one of them is zero and the slope of the other is undefined.
 
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