Triangles

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Triangles
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Take a rectangular piece of paper.
3
Take a rectangular piece of paper. Fold it in
half
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Take a rectangular piece of paper. Fold it in
half Use a ruler to draw a line from the top of
the fold to the bottom right hand corner.
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Take a rectangular piece of paper. Fold it in
half Use a ruler to draw a line from the top of
the fold to the bottom right hand corner. Cut
along the line.
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You should now have 3 triangles
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Can you prove that this is a line of symmetry?
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Does this triangle have any other line of
symmetry?
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No it doesnt. It only has the one.
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How can we prove that line ac is equal to line bc?
By folding along the line of symmetry. If you
havent tried it, do it now.
d
b
a
c
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d
b
a
b
This type of triangle, where two sides are equal,
has a special name. It is called an ISOSCELES
triangle
c
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d
b
a
b
Stick this triangle into your jotter and name it
ISOSCELES triangle. Now use the other two pieces
of the rectangle to make another isosceles
triangle.
c
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Your new triangle should look like this.
How do we know it is isoscles?
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Which of these triangles do you think is
isosceles?
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These are the isosceles triangles. Write in your
jotter how we can describe an isosceles triangle
and how we can prove it is isosceles.