The document defines and provides examples of different types of triangles based on their interior angles and side lengths. It explains that triangles can be classified as right, obtuse, or acute based on their interior angles, and as equilateral, isosceles, or scalene based on their side lengths. Examples are given of right scalene triangles, obtuse isosceles triangles, and acute scalene triangles to demonstrate how triangles can be classified based on both their angles and side lengths.

1. By That Math Lady
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2.  A triangle is a two-dimensional (flat) 3-sided
shape.
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3.  You can classify triangles by the
measurement of their interior angles.
 If a triangle has one 90° angle, it is called a
right triangle.
 If a triangle has one obtuse angle, it is called
an obtuse triangle.
 If a triangle has three acute angles, it is called
an acute triangle.
Let’s look at some examples of these
triangles…
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4.  A right triangle must have one angle that
measures 90° exactly.
90°
How do you know if an
angle is 90°? Place the corner
of a piece of paper in the angle.
If the border of the triangle aligns with
the sides of the paper, you know it is a
right angle!
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5.  An obtuse triangle must have one angle that
is greater than 90°.
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6.  An acute triangle has 3 acute angles. Each
angle must measure less than 90°.
What kind of sign
is this? What kind
of triangle?
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7.  You can classify triangles by the side lengths
and angle measurements.
 If a triangle has 3 equal side lengths, it is
called an equilateral triangle.
 If a triangle has 2 equal side lengths, it is
called an isosceles triangle.
 If a triangle has no equal side lengths, it is
called a scalene triangle.
Let’s look at some examples of these
triangles…
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8.  Equilateral triangles are made up of three
equal side lengths and three 60° angles. It
has three lines of symmetry.
60°
60° 60°
3 ft
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9.  Isosceles triangles are made up of two equal side
lengths and two equal angles. It has one line of
symmetry.
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10.  Scalene triangles are made up of 3 side
lengths and 3 angles that are all different
sizes and measurements. It does not have
any lines of symmetry.
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11.  It has a right angle…
 All the sides are different lengths...
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12. Yes! This is a right scalene triangle!
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13.  It has an obtuse angle…
 Two sides have identical lengths...
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14. Yes! This is an obtuse isosceles triangle!
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15.  It has three acute angles…
 All the sides have different lengths...
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16. Yes! This is an acute scalene triangle!
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17. Now You Know…
 how to classify triangles based on their
angles.
 how to classify triangles based on their side
lengths.
 words such as isosceles, scalene, and
equilateral.
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