How do you describe and perform translations, rotations, reflections and enlargements?
Describe and perform the four transformations (translation, rotation, reflection and enlargement, including negative and fractional scale factors at Higher tier) and combine them.
A focused answer to the Eduqas GCSE Mathematics geometry content on transformations, covering translation by a vector, rotation, reflection and enlargement including negative and fractional scale factors at Higher tier, and combining transformations.
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What this dot point is asking
The Eduqas geometry content asks you to describe and perform the four transformations: translation, rotation, reflection and enlargement, including negative and fractional scale factors at Higher tier, and to recognise the result of combining two of them. Transformations test both precise drawing and precise description, and Eduqas's "describe fully the single transformation" instruction demands the exact details that define each one. It appears at both tiers, with enlargement (especially negative and fractional factors) reaching into Higher.
Translation
A translation slides every point of a shape the same distance in the same direction, with no turning or resizing.
So a translation by moves the shape right and down. A full description needs only the word "translation" and the vector; the sign convention is the usual source of error, so check that down and left are negative.
Rotation
A rotation turns a shape about a fixed point.
A rotation is the same clockwise or anticlockwise, so the direction can be omitted only in that case. Tracing paper is the practical tool: place it over the shape, pin the centre, and turn. To describe a rotation fully, state all three details.
Reflection and enlargement
A reflection flips a shape across a mirror line, and an enlargement resizes it from a centre.
For an enlargement, each point moves so that its distance from the centre multiplies by the scale factor. A scale factor of triples every distance from the centre; a fractional factor such as halves them (a reduction). At Higher tier, a negative scale factor enlarges and places the image on the opposite side of the centre, effectively rotating it as well.
Combining transformations and describing fully
A combination of two transformations can sometimes be described as a single one, which Eduqas tests with "describe the single transformation equivalent to..." questions. The crucial exam skill is the full description: a translation needs its vector, a rotation needs angle, direction and centre, a reflection needs its mirror-line equation, and an enlargement needs its scale factor and centre. Giving only the type of transformation, without these details, loses marks even when the type is correct.
Exam-style practice questions
Practice questions written in the style of WJEC Eduqas exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Eduqas 20183 marksDescribe fully the single transformation that maps shape A onto shape B, where B is the same size and orientation as A but moved 4 units right and 3 units down. (Foundation, Component 1, non-calculator.)Show worked answer →
Same size and same orientation, only moved, means the transformation is a translation.
The movement is 4 right and 3 down, which as a column vector is .
A full description is: a translation by the vector .
Markers award a mark for identifying a translation and marks for the correct vector. Saying only "translation" without the vector, or giving the vector with the wrong sign on the downward movement, loses marks.
Eduqas 20224 marksShape P is enlarged by scale factor with centre of enlargement to give shape Q. Describe the effect on a point at and explain what the negative scale factor does. (Higher, Component 2, calculator.)Show worked answer →
A negative scale factor enlarges and also places the image on the opposite side of the centre.
The point is 2 units right of the centre . Scale factor sends it to units on the opposite side, so 4 units left of the centre, at .
The image is twice the size of P and inverted (rotated in effect) through the centre.
Markers give marks for the image point , for the doubling of size, and for explaining that the negative sign reflects the image to the opposite side of the centre. Treating as just (ignoring the sign) is the common error.
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Sources & how we know this
- WJEC Eduqas GCSE (9-1) Mathematics specification (C300) — WJEC Eduqas (2015)