Similar Triangles: Finding Area Ratio from Similarity Ratio of 7

Area Relationships with Similarity Ratios

The similarity ratio between two similar triangles is 7, so that the area ratio is —— _{——}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find the area ratio between the triangles
00:03 The triangles are similar according to the given data
00:09 The area ratio between the triangles equals the similarity ratio squared
00:22 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

The similarity ratio between two similar triangles is 7, so that the area ratio is —— _{——}

2

Step-by-step solution

We square it. 7 squared is equal to 49.

3

Final Answer

49

Key Points to Remember

Essential concepts to master this topic
  • Fundamental Rule: Area ratio equals similarity ratio squared
  • Key Calculation: Similarity ratio 7 gives area ratio 72=49 7^2 = 49
  • Verification: Check by comparing known side lengths: if sides are 7:1, areas are 49:1 ✓

Common Mistakes

Avoid these frequent errors
  • Using similarity ratio directly as area ratio
    Don't use 7 as the area ratio = wrong answer! Linear ratios don't apply to areas because area is two-dimensional. Always square the similarity ratio to get the correct area ratio.

Practice Quiz

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If it is known that both triangles are equilateral, are they therefore similar?

FAQ

Everything you need to know about this question

Why do I have to square the similarity ratio to get the area ratio?

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Because area is two-dimensional! If each side is 7 times longer, then both length and width are multiplied by 7, so area gets multiplied by 7×7=49 7 \times 7 = 49 .

What if the similarity ratio was a fraction like 1/3?

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You still square it! If similarity ratio is 13 \frac{1}{3} , then area ratio is (13)2=19 \left(\frac{1}{3}\right)^2 = \frac{1}{9} .

Does this rule work for all shapes, not just triangles?

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Yes! The area ratio equals similarity ratio squared for any similar shapes: triangles, rectangles, circles, or irregular polygons.

How can I remember this rule?

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Think of a simple example: if you double all sides of a square, the area becomes 4 times bigger, not 2 times! 22=4 2^2 = 4 .

What about volume ratios for 3D shapes?

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For similar 3D shapes, volume ratio equals similarity ratio cubed! If similarity ratio is 7, volume ratio would be 73=343 7^3 = 343 .

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