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- Year 9
Congruent triangles (SSS)
I can appreciate and use the criteria by which triangles are congruent (SSS).
- Year 9
Congruent triangles (SSS)
I can appreciate and use the criteria by which triangles are congruent (SSS).
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Lesson details
Key learning points
- By knowing the three side lengths of the triangle and its image, you can prove congruence.
- The corresponding angle pairs will be the same.
Keywords
Congruent - If one shape can fit exactly on top of another using rotation, reflection or translation, then the shapes are congruent.
Common misconception
Pupils may believe that as the sides fix the angles, that this implies it is true conversely.
Use any regular polygon to highlight that the angles will always be the same, but the edge lengths are not always the same length. Regular polygons are always similar but not necessarily congruent.
To help you plan your year 9 maths lesson on: Congruent triangles (SSS), download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 9 maths lesson on: Congruent triangles (SSS), download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 3 maths lessons from the Geometrical properties: similarity and Pythagoras' theorem unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
Licence
Prior knowledge starter quiz
6 Questions
Q1.In degrees, what is the size of the angle shown?

Q2.Select all the quadrilaterals that have at least one pair of equal sides.
Q3.These two rectangles are similar. This means that the side marked $$x$$ is cm.

Q4.Quadrilaterals ABCD and HEFG are congruent. Match each side or angle in quadrilateral ABCD with a corresponding edge or angle in quadrilateral HEFG.

AB -
GF
CD -
EH
BC -
EF
∠DCB -
∠FEH
∠ADC -
∠EHG
∠DAB -
∠HGF
Q5.A transformation has taken place on a shape. The image is congruent to the object. Which transformation cannot have taken place?
Q6.Match each quadrilateral with another quadrilateral that could have the same interior angles.
Square -
Rectangle
Parallelogram -
Rhombus
Isosceles trapezium -
Parallelogram
Kite -
Trapezium
Assessment exit quiz
6 Questions
Q1.If triangle ABC is congruent to triangle PQR. Match the corresponding equal edges.

AB -
QR
BC -
PR
AC -
QP
Q2.Triangle MNO is congruent to triangle ABC by SSS and MN is 11 cm. Which angle in triangle MNO is opposite MN?

Q3.Triangle MNO has two angles of 103° and 32°. Side MN is 12 cm. Are triangle ABC and MNO congruent?

Q4.STUV is a square. Match each statement to a reason to prove that triangle STU is congruent to triangle SVU by SSS.
ST = SV -
as ST and SV are both edges of the same square.
TU = VU -
as TU and VU are both edges of the same square.
SU -
is a common edge to both triangles.
Q5.Jun measures each of these triangles. Which of the triangles are congruent to this triangle by SSS?





Q6.PQRS is an isosceles trapezium. PR = QS. Match the letters in the proof with the correct edge.

a -
PQ
b -
QR
c -
PR