TRIANGLES PARTS, CLASSIFICATIONS, ANGLES NAD PROVING CONGRUENCE OF TRIANGLES.
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Transcript of TRIANGLES PARTS, CLASSIFICATIONS, ANGLES NAD PROVING CONGRUENCE OF TRIANGLES.
PARTS OF TRIANGLES
Sides the edges or boundaries of the triangle.
Vertices part where the two sides join.
Adjacent sides two sides that have common vertex
PARTS OF TRIANGLES
In a right triangleLegs
the sides adjacent to the right angle in a right triangle.
Hypotenuse the side opposite the right angle in a right angle.
PARTS OF TRIANGLES
In an isosceles triangle,Legs
-the congruent sidesBase
-the side that is not congruent to any side of an isosceles triangle.
Different Types of Triangles
There are several different types of triangles.
You can classify a triangle by its sides and its angles.
There are THREE different classifications for triangles based on their sides.
There are FOUR different classifications for triangles based on their angles.
Classifying Triangles by Their Sides
EQUILATERAL – 3 congruent sides
ISOSCELES – at least two sides congruent
SCALENE – no sides congruent
EQUILATERAL
ISOSCELES
SCALENE
Classifying Triangles by Their Angles
EQUIANGULAR – all angles are congruent
ACUTE – all angles are acute
RIGHT – one right angle
OBTUSE – one obtuse angle
EQUIANGULAR
ACUTE
RIGHT
OBTUSE
Congruent Triangles
What is "Congruent" ... ?It means that one shape can
become another using Turns, Flips and/or Slides:
ROTATION REFLECTION
TRANSLATION
Congruent Triangles
If two triangles are congruent they will have exactly the same three sides and exactly the same three angles.
The equal sides and angles may not be in the same position (if there is a turn or a flip), but they will be there.
Same Sides of a Triangle
If the sides are the same then the triangles are congruent. For example:
is congruent to and
because they all have exactly the same sides.
Same Sides of a Triangle
If the sides are the same then the triangles are congruent. For example:
is not congruent to
because the two triangles do not have exactly the same sides.
Same Angles of a Triangle
Does this also work with angles? Not always!
Two triangles can have the same angles but be different sizes:
is not congruent to
because, even though all angles match, one is larger than the
other.
Same Angles of a Triangle
Can two triangles of the same angles be congruent?
Yes. They could be congruent if they are the same size
is congruent to
because they are (in this case) the same size
Marking of Congruent Triangles
If two triangles are congruent, we often mark corresponding sides and angles like this:
is congruent to:
Marking of Congruent Triangles
The sides marked with one line are equal in length. Similarly for the sides marked with two lines and three lines.
The angles marked with one arc are equal in size. Similarly for the angles marked with two arcs and three arcs.
How To Find if Triangles are Congruent
Two triangles are congruent if they have:
exactly the same three sides and exactly the same three angles.
But we don't have to know all three sides and all three angles ...usually three out of the six is enough.
There are five ways to find if two triangles are congruent: SSS, SAS, ASA, AAS and HL.
1. SSS (side, side, side)
SSS stands for "side, side, side“ and means that we have two triangles with all three sides equal. For example:
is congruent to:
If three sides of one triangle are equal to three sides of another triangle, the triangles are congruent.
2. SAS (side, angle, side)
SAS stands for "side, angle, side" and means that we have two triangles where we know two sides and the included angle are equal.
For example:is congruent to:
If two sides and the included angle of one triangle are equal to the corresponding sides and angle of another triangle, the triangles are congruent.
3. ASA (angle, side, angle)
ASA stands for "angle, side, angle“ and means that we have two triangles where we know two angles and the included side are equal.
For example:is congruent to:
If two angles and the included side of one triangle are equal to the corresponding angles and side of another triangle, the triangles are congruent.
4. AAS (angle, angle, side)
AAS stands for "angle, angle, side“ and means that we have two triangles where we know two angles and the non-included side are equal.
For example:is congruent to:
If two angles and the non-included side of one triangle are equal to the corresponding angles and side of another triangle, the triangles are congruent.
5. HL (hypotenuse, leg)
HL stands for "Hypotenuse, Leg" (the longest side of the triangle is called the "hypotenuse", the other two sides are called "legs")
and
HL applies only to right angled-triangles!
5. HL (hypotenuse, leg) It means we have two right-angled
triangles with the same length of hypotenuse and the same length for one of the other
two legs. It doesn't matter which leg since the
triangles could be rotated. For example:
is congruent to If the hypotenuse and one leg of one right-angled triangle are equal to the corresponding hypotenuse and leg of another right-angled triangle, the two triangles are congruent.
Caution ! Don't Use "AAA" !
AAA means we are given all three angles of a triangle, but no sides.
This is not enough information to decide if two triangles are congruent!
Because the triangles can have the same angles but be different sizes:
For example: is congruent to
Without knowing at least one side, we can't be sure if two triangles are congruent..
Can You Classify the Different Triangles in the
Picture Below?
Classify the following triangles: AED, ABC, ACD, ACE