Mathematics
Grade 7
15 min
Area of triangles
Area of triangles
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1
Introduction & Learning Objectives
Learning Objectives
Identify the base and corresponding height of any triangle.
State and apply the formula for the area of a triangle.
Calculate the area of acute, right, and obtuse triangles given their base and height.
Solve real-world problems involving the area of triangles.
Correctly use and identify appropriate units for area measurements.
Explain the relationship between the area of a triangle and the area of a parallelogram.
Have you ever wondered how much paint you'd need for a triangular wall, or how much fabric for a triangular flag? 🚩
In this lesson, you'll discover the simple formula used to calculate the space inside any triangle. Understanding the area of triangles is a fundamental skill in geometry that helps us solve practical problems in design...
2
Key Concepts & Vocabulary
TermDefinitionExample
AreaThe amount of two-dimensional space a shape covers, measured in square units.If a square has sides of 1 cm, its area is 1 square centimeter (1 cm²).
TriangleA polygon with three sides and three angles.An equilateral triangle, an isosceles triangle, or a right triangle are all examples of triangles.
Base (of a triangle)Any side of a triangle that is chosen to be the 'bottom' for the purpose of calculating its area. It's usually denoted by 'b'.In a triangle, if you place it on one of its sides, that side can be considered the base.
Height (Altitude)The perpendicular distance from the chosen base to the opposite vertex (corner) of the triangle. It's denoted by 'h'.For a right triangle, one of the legs can be the height if the...
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Core Formulas
Area of a Triangle Formula
$$A = \frac{1}{2} \times b \times h$$
This formula calculates the area (A) of any triangle, where 'b' represents the length of the base and 'h' represents the corresponding height (altitude) perpendicular to that base.
Identifying Base and Height
The height 'h' must always be the perpendicular distance from the chosen base 'b' to the opposite vertex. For right triangles, the legs can serve as base and height. For obtuse triangles, the height may fall outside the triangle, requiring the base to be extended.
Correctly identifying the base and its corresponding perpendicular height is crucial for accurate area calculations. The height is never a slanted side unless it's a leg of a right triangle.
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Challenging
A triangle has an area of 64 cm². Its base and height are equal in length. What is the length of its base?
A.8 cm
B.16 cm
C.11.3 cm
D.12 cm
Challenging
A shape is made of a square with 8-inch sides and an isosceles triangle attached to one side of the square. The total height of the entire shape is 14 inches. What is the total area of the shape?
A.112 in²
B.88 in²
C.96 in²
D.176 in²
Challenging
The base of a triangle is doubled, and its height is also doubled. How does the area of the new triangle compare to the area of the original triangle?
A.It is 2 times larger.
B.It is 4 times larger.
C.It is 8 times larger.
D.It is the same size.
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