Plane Figure: A flat, two-dimensional shape that exists on a plane (flat surface).
2D Shape: A shape that has only length and width, but no depth.
Side: One of the straight lines that make up a shape.
Vertex (plural: vertices): A corner where two sides meet.
Angle: The space between two connected sides, measured in degrees.
Right angle: An angle that measures exactly 90° (like the corner of a square).
Parallel lines: Lines that never meet, always stay the same distance apart.
• Plane figures are flat (2-dimensional)
• They have length and width only
• They exist on a flat surface (plane)
• They have boundaries made of lines or curves
• They enclose an area
• They can be measured in terms of perimeter and area
Step 1: Read the problem carefully
Step 2: Identify what you need to find
Step 3: List known facts about the shape(s)
Step 4: Apply geometric properties and rules
Step 5: Solve step by step
Step 6: Check your answer
Step 7: Write the final answer
• Plane: Think "FLAT" - like an airplane wing (but flat!)
• 2D: Two Dimensions - Length and Width only
• Quadrilateral: Quad means 4, so 4 sides
• Triangle: Tri means 3, so 3 sides
• Polygon: Poly means many, so many sides
Question: Sarah has a rectangular garden that is 6 feet long and 4 feet wide. What is the perimeter of her garden?
Solution: Perimeter = 2 × (length + width) = 2 × (6 + 4) = 2 × 10 = 20 feet
Answer: 20 feet
Question: A square has sides that are 5 inches long. What is the area of the square?
Solution: Area = side × side = 5 × 5 = 25 square inches
Answer: 25 square inches
Question: Tom sees a shape with 4 equal sides and 4 right angles. What shape is it?
Solution: A shape with 4 equal sides and 4 right angles is a square.
Answer: Square
Question: A triangle has sides measuring 3 cm, 4 cm, and 5 cm. What type of triangle is this?
Solution: All sides are different lengths, so it's a scalene triangle.
Answer: Scalene triangle
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Problem: A rectangle has a perimeter of 24 cm. If one side is 5 cm, what is the length of the other side?
Perimeter = 2 × (length + width)
24 = 2 × (5 + width)
24 = 10 + 2 × width
24 - 10 = 2 × width
14 = 2 × width
width = 7 cm
Problem: A shape has 4 sides. Two sides are 6 cm long, and two sides are 4 cm long. The angles are all 90°. What shape is it?
• 4 sides (quadrilateral)
• Two pairs of equal sides (6 cm and 4 cm)
• All angles are 90°
A quadrilateral with opposite sides equal and all angles 90° is a rectangle.
Rectangles have 2 pairs of equal opposite sides and 4 right angles.
Problem: Which has a larger area: a square with sides of 6 cm or a rectangle with sides of 4 cm and 8 cm?
Area of square = 6 × 6 = 36 square cm
Area of rectangle = 4 × 8 = 32 square cm
36 > 32, so the square has a larger area.