Free sample · Sec 1
G3 Sec 1 G1 Angles, triangles and polygons
Angles, triangles and polygons. Five printed grains — name the angle job, then find the missing angle.
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1.1 angle types
Look at the four openings. Compare each width to a square corner and to a straight line. A square corner is a right angle. Smaller than a right angle is acute. Wider than a right angle but less than a straight line is obtuse. Past a straight line is reflex. Name the type of gap first, then you know which missing angle you are after.
1.2 angle facts
Before you chase a number, name the angle job on the figure. Look at the crossing. Facing angles across the X are vertically opposite — they are equal. Angles that sit together on one straight line add to 180 degrees. Angles that fill one point add to 360 degrees. Name the job first, then use equal, 180, or 360 to find the missing angle.
1.3 parallel lines
Look at the two parallel lines and the transversal that cuts them. Same corner place at both crossings: corresponding angles — they are equal. The Z pair between the parallels: alternate angles — they are equal. Between the parallels on the same side of the cut: co-interior angles — they add to 180 degrees. Name the pair first, then use equal or add to 180 degrees to find the missing angle.
1.4 named regular polygons
Look at the regular pentagon, hexagon, octagon, and decagon. Regular means every side is the same length and every interior angle is the same size. That matching is the symmetry. Name the shape first. Then a missing side equals any known side, and a missing interior angle equals any known interior angle.
1.6 interior/exterior angle sum
A convex hexagon — corners inside, turns outside.
Name interior or exterior, then use that sum.
Look at any convex polygon. Interior angles sit at the corners inside. Exterior angles are the outside turns as you walk around the shape. Exterior sum = 360° for every convex polygon. Interior sum depends on the number of sides. Name interior or exterior, then use that sum.
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