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CCSS.Math:

we're asked to draw the line of reflection that reflects triangle ABC so that's this blue triangle onto triangle a prime B prime C prime which is this red triangle right over here and they give us a little line drawing tool in order to draw the line of reflection so the way I'm gonna think about it is well when I just eyeball it they look it looks like I'm just flipped over some type of a horizontal line here but let's see if we can actually construct a horizontal line where it does actually look like the line of reflection so let's see C and C Prime how far apart are they from each other so if we go one two three four five six down so they are six apart so let's see if we just put this three above C Prime and three below C let's see if this horizontal line works as a line of reflection so C or C prime is definitely the reflection of C across this line C is exactly three units above it and C prime is exactly three units below it let's see if it works for a and a prime a is one two three four five units above it a prime is one two three four five units below it so that's looking good now let's just check out B so B we can see it's at the y coordinate here is seven this line right over here is y is equal to one and so what we would have here is let's see this is looks like it's six units above this line and B prime is six units below the line so this indeed works we've just constructed the line of reflection that reflects the blue triangle triangle ABC on to triangle a prime B prime C Prime