Video Summary - Grade 5 MATH –Term 1 Week 7 Base & Height of a Parallelogram, Triangle, and Trapezoid

Main ideas and lessons

The lesson focuses on Grade 5 math: finding base and height and using them to compute area for:
- Parallelograms
- Triangles
- Trapezoids
A key challenge is that shapes may be shown in different orientations (rotated/turned), so base and height are not always “easy-looking” until students correctly identify them.
Students learn that:
- Height is always the perpendicular distance from the base to the opposite side (or the opposite parallel side), creating a right angle.
- The choice of base affects the height, because height depends on which side is treated as the base.
The lesson includes vocabulary and repeated practice using area formulas.

Identify the height of a parallelogram, triangle, and trapezoid in different orientations.
Find the area of each shape using the correct formula, expressing answers in:
- square centimeters (cm²) or
- square meters (m²)

Square unit / linear unit
- A square unit is one unit of area.
- A linear unit refers to side length (the number of units along an edge).
Area
- The number of square units that cover the surface of a figure.
Triangle
- A three-sided polygon.
Parallelogram
- A four-sided polygon with two pairs of opposite sides parallel.
Trapezoid
- A four-sided polygon with one pair of opposite sides parallel.
Height definitions (perpendicular distance)
- Triangle height: the length of a perpendicular line segment from a vertex to the opposite side.
- Parallelogram / trapezoid height: the length of the perpendicular line from the base line to the line parallel to it.

Short review: in standard orientation, students can see:
- Base = horizontal bottom side
- Height = vertical side pointing up (like a building/flagpole)
“Level up” idea:
- The same shapes appear turned.
- Students must still identify:
  - the base
  - the height (perpendicular distance)
Shapes referenced during the challenge:
- Parallelogram
- Triangle
- Trapezoid

How to draw triangle height
- Draw a straight perpendicular line (right angle) from the vertex to the opposite side (base).
- The height is the length of that perpendicular line.
What changes when the base changes
- If a different side is treated as the base, the perpendicular height changes.
Key rule
- A triangle has three possible heights, depending on which side is chosen as the base:
  - Height from point C down to side AB
  - Height from point B down to side CA
  - Height from point A down to side BC

Rule
- The parallelogram’s height is the perpendicular distance from the chosen base to the opposite parallel side.
Students are prompted to “answer based on” the chosen base side (example naming indicates different base choices).

What makes a trapezoid
- Only one pair of opposite sides are parallel → those parallel sides are the bases.
Height of a trapezoid
- The height is the perpendicular distance between the two parallel sides.
- Even if either parallel side is considered the “base,” the height stays the same because it’s the same distance between the parallel lines.
Instruction idea
- Identify the two parallel sides first; the height is perpendicular to both.

Students work with multiple figures where base and height measurements are given (e.g., triangles/parallelograms/trapezoids).
Emphasis:
- height depends on the selected base
- the height must be perpendicular to the base

Parallelogram area
- Formula: ( A = B \times H )
- Example:
  - Base = 20 cm, Height = 12 cm
  - ( A = 20 \times 12 = 240 ) cm²
Triangle area
- Formula: ( A = \dfrac{B \times H}{2} )
- Example:
  - Base = 16 m, Height = 15 m
  - ( A = \dfrac{16 \times 15}{2} = \dfrac{240}{2} = 120 ) m²
Trapezoid area
- Formula: ( A = \dfrac{(B_1 + B_2)\times H}{2} )
- Example:
  - Bases = 18 cm and 12 cm, Height = 8 cm
  - The worked result is stated as 80 cm² in the later example section.

Parallelogram
- Locate the height
  - Find the straight line from the top to the bottom base that makes a 90° right angle.
- Find the area
  - Use: ( A = B \times H )
Triangle
- Find the height
  - Draw a straight perpendicular line from the top vertex to the base that makes a right angle.
- Find the area
  - Use: ( A = \dfrac{B \times H}{2} )
Trapezoid
- Find the height
  - The height may not be directly shown.
  - If you know the diagonals, use them to determine the missing height.
  - Check diagonal length information.
- Find the area
  - Use: ( A = \dfrac{(B_1 + B_2)\times H}{2} )