CONGRUENT

TRIA

NGLES

UN

I T 2

LE

SS

ON

1

Triangle Style

WHAT IS CONGRUENCY?

When two shapes are exactly the same size and shape we say they are CONGRUENT

WHICH OF THESE SHAPES IS CONGRUENT WITH THE FIRST SHAPE?

Even though their direction changed, they are the same size and shape.

Too small

Too big

WHICH OF THE FOLLOWING ARE CONGRUENT?

WHICH OF THE FOLLOWING ARE CONGRUENT?

THERE ARE 5 CONDITIONS WE CAN USE TO DETERMINE IF 2 TRIANGLES ARE CONGRUENT

• SSS -- Side-Side-Side• SAS – Side-Angle-Side• ASA – Angle-Side-Angle• AAS – Angle-Angle-Side• RHS – Right-Hypotenuse-Side

WHY DO THEY WORK?

These rules work because they show us the MINIMUM information we need to know to be able to use Geometry to determine the remaining angles and side lengths. Therefore, if we memorize these rules, we

can know immediately if triangles are congruent or not.

SIDE – SIDE – SIDE

Just like for the images, if all the sides of a triangle are the same, then that must mean that the triangles are congruent.

This is known as the Side-Side-Side condition or SSS

SIDE – ANGLE – SIDE

If you know two sides and a single angle, we can determine the final leg length and angles, therefore we know these angles must be congruent.

This is known as the Side-Angle-Side condition or SAS

ANGLE – SIDE – ANGLE

If we know two angles and a side we can use geometry to determine the other angles and sides, therefore we can determine that the triangles have the same angles and side lengths. Therefore we only need to know 2 angles and 1 side to determine that the triangles are congruent.

This is known as the Angle-Side-Angle condition or ASA

ANGLE – ANGLE – SIDE

If we know two angles and a side we can use geometry to determine the other angles and sides, therefore we can determine that the triangles have the same angles and side lengths. Therefore we only need to know 2 angles and 1 side to determine that the triangles are congruent.

This is known as the Angle-Angle-Side condition or AAS

RIGHT – HYPOTENUSE – SIDE

If we know one angle is a right angle, and we know the hypotenuse and a side, we can determine the rest of the angles and sides using geometry. Therefore we only need to know that there is a right angle and the lengths of the hypotenuse and one side to determine the triangles are congruent.

This is known as the Right Hypotenuse Side condition RHS

RULES THAT

DON’T WORK

ANGLE – ANGLE – ANGLE

If all angles are the same that does not mean they are congruent. The leg lengths could be different.

SIDE – SIDE – ANGLE

Even if we know two sides and an angle, we do not have enough information to determine the rest of the triangle’s features.

PRACTICE – ARE THESE CONGRUENT? IF SO BY WHICH CONDITION?

PRACTICE – ARE THESE CONGRUENT? IF SO BY WHICH CONDITION?

YES-ASA

NO- AAA IS NOT A CONDITION FOR CONGRUENCY.

NO –SSA IS NOT A CONDITION FOR CONGRUENCY

YES- SSS

YES - SAS

YES- AAS

YES – RHS