Mathematics Grade 7 15 min

Area of compound figures with triangles, semicircles, and quarter circles

Area of compound figures with triangles, semicircles, and quarter circles

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Introduction & Learning Objectives

Learning Objectives Identify the basic geometric shapes (triangles, semicircles, quarter circles) within a compound figure. Recall and apply the area formulas for triangles, semicircles, and quarter circles. Decompose complex compound figures into simpler, familiar shapes. Calculate the area of each component shape accurately. Combine (add or subtract) the areas of component shapes to find the total area of a compound figure. Solve real-world problems involving the area of compound figures. Ever wondered how much paint you'd need for a uniquely shaped wall, or how much grass seed for a garden with curved edges? 🤔 It's all about breaking down complex shapes! In this lesson, you'll learn how to find the area of figures made up of triangles, semicircles, and qu...
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Key Concepts & Vocabulary

TermDefinitionExample Compound FigureA geometric shape that is formed by combining two or more basic geometric shapes, such as triangles, rectangles, circles, or parts of circles.A house shape made by putting a triangle (roof) on top of a rectangle (walls). AreaThe amount of two-dimensional space a shape or surface covers, measured in square units (e.g., square inches, square meters).The area of a square with sides of 5 cm is 25 square centimeters (25 cm²). TriangleA polygon with three straight sides and three angles. Its area depends on its base and height.A right triangle with a base of 4 units and a height of 3 units. SemicircleExactly half of a circle. Its area is half the area of a full circle with the same radius.The shape of a rainbow or half of a pizza. Quarter CircleExactly one-f...
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Core Formulas

Area of a Triangle $$A = \frac{1}{2}bh$$ Use this formula to find the area of any triangle, where 'b' is the length of the base and 'h' is the perpendicular height from the base to the opposite vertex. Area of a Semicircle $$A = \frac{1}{2}\pi r^2$$ Use this formula to find the area of a semicircle, where 'r' is the radius of the full circle from which the semicircle is formed. Remember to use $\pi \approx 3.14$ for calculations. Area of a Quarter Circle $$A = \frac{1}{4}\pi r^2$$ Use this formula to find the area of a quarter circle, where 'r' is the radius of the full circle from which the quarter circle is formed. Remember to use $\pi \approx 3.14$ for calculations.

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Sample Practice Questions

Challenging
A semicircle has a diameter of 24 cm. An isosceles triangle is inscribed inside it, with the diameter as its base. Find the area of the region that is inside the semicircle but outside the triangle. (Use π ≈ 3.14)
A.82.08 cm²
B.226.08 cm²
C.144 cm²
D.370.08 cm²
Challenging
Inside a square with a side length of 10 cm, two quarter circles are drawn, each with a radius of 10 cm, from opposite corners. What is the area of the overlapping 'leaf' shape? (Use π ≈ 3.14)
A.100 cm²
B.57 cm²
C.78.5 cm²
D.28.5 cm²
Challenging
A compound figure made of a triangle and a semicircle has a total area of 40 in². If all of its linear dimensions (base, height, radius) are tripled, what will be the new area?
A.40 in²
B.120 in²
C.240 in²
D.360 in²

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