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## Basic geometry and measurement

### Course: Basic geometry and measurement>Unit 14

Lesson 4: Reflections

# Reflecting points

We can plot points after reflecting them across a line, like the x-axis or y-axis. Reflections create mirror images of points, keeping the same distance from the line. When we reflect across the y-axis, the image point is the same height, but has the opposite position from left to right.

## Want to join the conversation?

• What does prime mean when for example they say C prime?
• In the context of geometric transformations, the prime symbol (') denotes the image of a point as a result of a transformation. For example, point A' is the image of point A, point B' is the image of point B, and point C' is the image of point C.

Eventually, you might see prime symbols in other mathematical contexts as well. For example, in calculus, if f is a function, then f' denotes the derivative (instantaneous rate of change) of the function f.
• Is there a video that shows how to reflect a point over a diagonal line? I am really confused because I thought that there was a formula to do so.
• how do you identify the reflection of -2,6 ?
• Depends what axis you are reflecting over, if you are reflecting over x axis, change the y positive or negative sign to the opposite sign, if it reflects over y axis, change the sign of the x.
Hope this helps
• why do we do this
• legit no idea
• if it helps reference stranger things. the Upside Down mirrors the actual world. Then imagine Will Byers from stranger things as a shape/ figure undergoing reflection. Simplified, i would describe a trip to the Upside Down a reflection in mathematical terms
• Lol im in 6th grade and i understand this better than eighth graders
• Nice, I'm in 6th grade too I can't say I'm better than 8th graders but I too am studying 8th grader stuff. It's way more interesting than boring gr 6 stuff.
• Thanks! there's actually a way to do it algebraically too, if you don't know it already you'll need it: Across the x-axis -(x,y)- (x,-y)
Across the y-axis- (x,y) - (-x, y)
Just follow this rule and you won't even need a graph to know a reflection!
• This was fairly easy thank you for making this so i can understand it better.