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Lines of Symmetry
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 We'll learn that a line of symmetry cuts a shape into 2 matching halves.
 We'll also learn how to identify lines of symmetry.
 And we'll see that we can find symmetry in animals, plants, and items we use everyday!

Discussion Questions

Before VideoHow do you describe a rectangle?ANSWER

A rectangle is a 4sided shape that has two sets of parallel lines that connect at right angles.

A square is a type of rectangle with 4 sides of equal length.

A parallelogram is a 4sided shape that has two sets of parallel lines.

No. All squares are rectangles, but not all rectangles are squares!

No. All rectangles are parallelograms, but not all parallelograms are rectangles!


After VideoDoes every object have a line of symmetry?ANSWER

No. Some objects have no lines of symmetry, some have 1 line, and some have more.

Answers may vary.

Answers may vary.

If letters are written very simply, then these have 1 line of symmetry: A, B, C, D, E, M.
These have 2 lines of symmetry: I, O, H, X.
These have none: F, G, J, L, N.

No. A circle has an infinite number of lines of symmetry, but the line must go through the center of the circle. So the circle must be folded in half.



Vocabulary

Mirror Image
DEFINE
A flipped version of an image, like you would see on the other side of a mirror.

Symmetry
DEFINE
A shape has symmetry if it can be divided by a line so that each half is a mirror image of the other.

Line of Symmetry
DEFINE
The line that divides a shape into two mirror images.

Rectangle
DEFINE
A 4sided shape that has two sets of parallel lines that connect at right angles.

Square
DEFINE
A type of rectangle with 4 sides of equal length.

Parallelogram
DEFINE
A 4sided shape that has two sets of parallel lines.

Diagonally
DEFINE
Connecting two opposite corners.

Infinite
DEFINE
Going on forever; more than we could ever count.

Mirror Image
DEFINE

Reading Material
Download as PDF Download PDF View as Separate PageWHAT ARE LINES OF SYMMETRY?A shape has symmetry if it can be divided by a line so that each half is a mirror image of the other. A line of symmetry is a line that divides a shape in that way.
To better understand lines of symmetry…
WHAT ARE LINES OF SYMMETRY?. A shape has symmetry if it can be divided by a line so that each half is a mirror image of the other. A line of symmetry is a line that divides a shape in that way. To better understand lines of symmetry…LET’S BREAK IT DOWN!
Faces
Adesina has a red paper heart. Marcos folds the paper heart in half and April notices that the two sides match. We learn that a shape has symmetry if it can be divided by a line so that each half is a mirror image of the other. The line that divides the shape is called the line of symmetry. If we draw a line down the middle (from top to bottom) of a person’s or animal’s face, we can see that faces are mostly symmetrical too. If we try to split a face in half by drawing a line from left to right, we see that the two halves do not match: they are not mirror images. So, the line drawn from top to bottom is a line of symmetry, but the line drawn from left to right is not a line of symmetry. If we draw a line dividing an image of a butterfly into a left half and a right half, both sides are mirror images, so the line is a line of symmetry. If we draw the line across, the top half does not match the bottom half: the top has antennas but the bottom does not. Then the line across is not a line of symmetry. Some objects have many lines of symmetry. A 3leaf clover has 3 lines of symmetry. Now you try: Can you think of something in the real world that has two lines of symmetry?
Faces Adesina has a red paper heart. Marcos folds the paper heart in half and April notices that the two sides match. We learn that a shape has symmetry if it can be divided by a line so that each half is a mirror image of the other. The line that divides the shape is called the line of symmetry. If we draw a line down the middle (from top to bottom) of a person’s or animal’s face, we can see that faces are mostly symmetrical too. If we try to split a face in half by drawing a line from left to right, we see that the two halves do not match: they are not mirror images. So, the line drawn from top to bottom is a line of symmetry, but the line drawn from left to right is not a line of symmetry. If we draw a line dividing an image of a butterfly into a left half and a right half, both sides are mirror images, so the line is a line of symmetry. If we draw the line across, the top half does not match the bottom half: the top has antennas but the bottom does not. Then the line across is not a line of symmetry. Some objects have many lines of symmetry. A 3leaf clover has 3 lines of symmetry. Now you try: Can you think of something in the real world that has two lines of symmetry?Symmetry in Shapes
Adesina folds a cutout rectangle in half from top to bottom and the edges of the two halves match up perfectly. This means that the fold is a line of symmetry. She unfolds the rectangle and then folds it from left to right and the edges of the two halves match up again. This rectangle has two lines of symmetry. When she folds the rectangle diagonally, the edges of the two halves do not match up. The diagonal line is not a line of symmetry on a rectangle. We discover that a square has two diagonal lines of symmetry, as well as the folds from top to bottom and left to right. We discover that a parallelogram does not have symmetry because the edges do not match up, no matter how we fold it. Only parallelograms that are rectangles have symmetry, and only parallelograms that are squares have 4 lines of symmetry. Now you try: What is a letter of the alphabet that has no lines of symmetry?
Symmetry in Shapes Adesina folds a cutout rectangle in half from top to bottom and the edges of the two halves match up perfectly. This means that the fold is a line of symmetry. She unfolds the rectangle and then folds it from left to right and the edges of the two halves match up again. This rectangle has two lines of symmetry. When she folds the rectangle diagonally, the edges of the two halves do not match up. The diagonal line is not a line of symmetry on a rectangle. We discover that a square has two diagonal lines of symmetry, as well as the folds from top to bottom and left to right. We discover that a parallelogram does not have symmetry because the edges do not match up, no matter how we fold it. Only parallelograms that are rectangles have symmetry, and only parallelograms that are squares have 4 lines of symmetry. Now you try: What is a letter of the alphabet that has no lines of symmetry?Drawing Using Lines of Symmetry
Take a piece of grid paper and fold it along one of the grid lines. Now, think of something simple to draw using straight lines, and draw exactly half of it on one side of the folded line. Color it in, and switch drawings with a partner. Finish their image by drawing the mirror image on the other side of the fold line. April draws a house and notices that if a line is 4 grid lines to the left of the fold on one side, its mirror image will be exactly 4 grid lines to the right of the fold on the other side. Every part of the drawing on the left side must be the same distance from the fold as the matching parts of the drawing on the right side. Lastly, we learn that a circle has an infinite number of lines of symmetry if it is folded exactly through the middle. Now you try: Do the drawing activity on your own. Fold a piece of grid paper along a line, and think of a simple image to draw. Draw half of it on one side of the line, and then complete the drawing by creating the mirror image on the other side. Do they match?
Drawing Using Lines of Symmetry Take a piece of grid paper and fold it along one of the grid lines. Now, think of something simple to draw using straight lines, and draw exactly half of it on one side of the folded line. Color it in, and switch drawings with a partner. Finish their image by drawing the mirror image on the other side of the fold line. April draws a house and notices that if a line is 4 grid lines to the left of the fold on one side, its mirror image will be exactly 4 grid lines to the right of the fold on the other side. Every part of the drawing on the left side must be the same distance from the fold as the matching parts of the drawing on the right side. Lastly, we learn that a circle has an infinite number of lines of symmetry if it is folded exactly through the middle. Now you try: Do the drawing activity on your own. Fold a piece of grid paper along a line, and think of a simple image to draw. Draw half of it on one side of the line, and then complete the drawing by creating the mirror image on the other side. Do they match? 
Practice Word Problems

Practice Number Problems

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Science & Math$_{/yr}

Science Only$_{/yr}
How many lines of symmetry does the letter M have?
What is a letter that has no lines of symmetry?
Draw a shape that has 4 lines of symmetry and draw the lines of symmetry.
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