Cogito
Grade 6 Math · Chapter 7 · Lesson 1
Area of Triangles
Half of the rectangle around it.
10 problems · about 17 minutes · 6.G.A.1
What this lesson teaches
The child finds the area of a triangle by relating it to a rectangle.
- A triangle is half the rectangle with the same base and height.
- Area is half the base times the height.
- The height is perpendicular to the base, not a side.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Two Variables That Move Together: If y = 5x, what is y when x is 8?
Answer 40
Why 40.
Review — Inequalities on a Number Line: Smallest whole number satisfying x > 11?
Answer 12
Why 12.
Warm Up
Straightforward practice. Get the method working first.
4 problemsBase 14, height 6. Area?
Answer 42
Why 42.
What is the height of a triangle?
Answer The perpendicular distance from the base.
Why Height is measured at a right angle to the base.
Base 6, height 4. Area?
Answer 12
Why 24 halved.
Base 9, height 10. Area?
Answer 45
Why 90 halved.
Build It Up
The same ideas with more to keep track of.
2 problemsArea 35, base 7. Height?
Answer 10
Why 70 ÷ 7.
Base 5, height 12. Area?
Answer 30
Why 60 halved.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Sail: A triangle with base 12 and height 5. What is its area?
Answer 30 square units
Why 30.
The Missing Height: A triangle has area 24 and base 8. What is its height?
Answer 6
Why 48 ÷ 8 = 6.