In Pre-algebra we learnt that triangles have three sides and
three angles. We also learnt that the sum of the angles in a
triangle is 180°.
If two triangles have the same size and shape they are called
congruent triangles. If we flip, turn or rotate one of two
congruent triangles they are still congruent.
If the sides of two triangles are the same then the triangles
must have the same angles and therefore must be congruent. We can
tell just from knowing the sides if two triangles are congruent or
If we know that two sides of a triangle and the angle between
them are congruent to two sides and the angle between them of
another triangle then these two triangles are also congruent.
Likewise if we know that two angles and the side between them
are congruent to two angles and the side between them in another
triangle then these two triangles are also congruent.
The last case that gives us congruent triangles is when two
angles and a nonincluded side in one triangle are congruent to the
corresponding angles and side of another triangle.
Video lesson: Find the values of x and y so
that the triangles are congruent.