Constructions

    OCR
    GCSE

    Constructions require the precise use of a straightedge and pair of compasses to generate geometric figures and loci without reliance on measurement tools like protractors. Candidates must demonstrate mastery of the four standard constructions: perpendicular bisector of a line segment, perpendicular to a line from a given point, bisector of an angle, and construction of specific angles (e.g., 60°, 90°). Crucially, examiners require all construction arcs to remain visible to evidence the geometric method used; responses where arcs are erased or missing are penalized even if the final line is accurate. Advanced applications involve defining loci to identify regions satisfying multiple inequalities, often within complex scale drawing contexts.

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    Objectives
    3
    Exam Tips
    3
    Pitfalls
    4
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award method marks for visible intersecting arcs drawn with a compass; freehand sketches or protractor use score zero where 'Construct' is commanded
    • Award 1 mark for the perpendicular bisector drawn within ±2mm tolerance of the midpoint and ±2° of perpendicularity
    • Award 1 mark for the angle bisector drawn within ±2° tolerance, originating correctly from the vertex
    • Credit the correct region shaded that satisfies all boundary conditions in loci problems

    Marking Points

    Key points examiners look for in your answers

    • Award method marks for visible intersecting arcs drawn with a compass; freehand sketches or protractor use score zero where 'Construct' is commanded
    • Award 1 mark for the perpendicular bisector drawn within ±2mm tolerance of the midpoint and ±2° of perpendicularity
    • Award 1 mark for the angle bisector drawn within ±2° tolerance, originating correctly from the vertex
    • Credit the correct region shaded that satisfies all boundary conditions in loci problems

    Examiner Tips

    Expert advice for maximising your marks

    • 💡If the question says 'Construct', you must use a pair of compasses; using a protractor or set square will not earn full marks even if the result is accurate
    • 💡Leave all construction lines visible; examiners treat these as your 'working out' and often award marks for them even if the final line is slightly inaccurate
    • 💡Ensure your compass pencil is sharp and the hinge is tight; loose compasses slip during rotation, leading to accuracy penalties outside the ±2mm tolerance

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Erasing construction arcs after drawing the final line, which removes the evidence required for method marks
    • Using a protractor to measure and mark an angle (e.g., 60°) when the command word is 'Construct', resulting in zero marks
    • Confusing the locus equidistant from two points (perpendicular bisector) with the locus equidistant from two lines (angle bisector)

    Study Guide Available

    Comprehensive revision notes & examples

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    Key Terminology

    Essential terms to know

    Standard constructions (perpendicular and angle bisectors)
    Loci and regions satisfying inequalities
    Construction of triangles (SSS, SAS, ASA) and polygons
    Scale drawings and bearings integration

    Likely Command Words

    How questions on this topic are typically asked

    Construct
    Draw
    Shade
    Describe
    Show

    Practical Links

    Related required practicals

    • •{"code":"Geometrical Instruments","title":"Usage of ruler and compasses","relevance":"Essential for all construction tasks to ensure precision"}

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