Question P5 Angle and shape properties
Three interior angles of a quadrilateral are 70°, 115° and 80°. Find the fourth angle.
Answer
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Mark the shape property first, then subtract known angles from the relevant total.
In this one. A quadrilateral can be split into two triangles, which explains its 360° angle total.
Look for a named quadrilateral like a rhombus or parallelogram, plus two straight lines crossing inside or through it. Words like "straight line" and "collinear" point to this move.
Children mix up which angle sits opposite which once lines cross at a point away from the main shape. Trace each ray back to its two labelled ends before deciding what faces what.
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