Using the image shown, name the reflection image of the point (2,1) over the y-axis. Your answer should be in (x,y) notation with no spaces.



A. (2,-1)

B. (-1,-2)

C. (-1,2)

D. (-2,1)



Is this true or false?


Perpendicular lines have the same slopes.


A. true

B. false

 Mar 9, 2020
edited by macabresubwoofer  Mar 9, 2020

The correct answer is D: (-2,1) because the position of the point before the reflection is 2 units to the right of the y-axis and 1 unit above the x-axis. Reflecting the point across the y-axis does not change the position relative to the x-axis. It also does not change the number of units away from the y-axis, only the direction away, so instead of 2 units to the right, the point will be 2 units to the left, at the position (-2,1). 


It is false that perpendicular lines hae the same slopes. Parallel lines have the same slope, perpendicular lines have opposite slopes. The slopes of perpendicular lines are negative reciprocals. For example, if line A has a slope of 2, then line B, which is perpendicular to line A, will have a slope of \(-{1 \over 2}\)


I hope this is helpful to you.


 Mar 9, 2020

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