Rectangle ABCD: Finding Diagonal Length m with Side Ratio √(x/2)

Pythagorean Theorem with Square Root Ratios

Given the rectangle ABCD

AB=X the ratio between AB and BC is equal tox2 \sqrt{\frac{x}{2}}

We mark the length of the diagonal A A with m m

Check the correct argument:

XXXmmmAAABBBCCCDDD

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Mark the correct statement
00:03 Side ratio according to the given data
00:11 Insert appropriate values into the expression and solve to find BC
00:17 Make sure to extract the root for both the numerator and denominator
00:30 Isolate BC
00:38 Factor X into the square root of X multiplied by the square root of X
00:44 Simplify wherever possible
00:49 This is the length of side BC
01:03 Use the Pythagorean theorem in triangle ABC
01:10 Insert the appropriate values into the expression and solve
01:25 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Given the rectangle ABCD

AB=X the ratio between AB and BC is equal tox2 \sqrt{\frac{x}{2}}

We mark the length of the diagonal A A with m m

Check the correct argument:

XXXmmmAAABBBCCCDDD

2

Step-by-step solution

Let's find side BC

Based on what we're given:

ABBC=xBC=x2 \frac{AB}{BC}=\frac{x}{BC}=\sqrt{\frac{x}{2}}

xBC=x2 \frac{x}{BC}=\frac{\sqrt{x}}{\sqrt{2}}

2x=xBC \sqrt{2}x=\sqrt{x}BC

Let's divide by square root x:

2×xx=BC \frac{\sqrt{2}\times x}{\sqrt{x}}=BC

2×x×xx=BC \frac{\sqrt{2}\times\sqrt{x}\times\sqrt{x}}{\sqrt{x}}=BC

Let's reduce the numerator and denominator by square root x:

2x=BC \sqrt{2}\sqrt{x}=BC

We'll use the Pythagorean theorem to calculate the area of triangle ABC:

AB2+BC2=AC2 AB^2+BC^2=AC^2

Let's substitute what we're given:

x2+(2x)2=m2 x^2+(\sqrt{2}\sqrt{x})^2=m^2

x2+2x=m2 x^2+2x=m^2

3

Final Answer

x2+2x=m2 x^2+2x=m^2

Key Points to Remember

Essential concepts to master this topic
  • Ratio Analysis: Convert given ratio to find the unknown side length
  • Technique: From xBC=x2 \frac{x}{BC} = \sqrt{\frac{x}{2}} , solve to get BC=2x BC = \sqrt{2x}
  • Check: Verify using Pythagorean theorem: x2+2x=m2 x^2 + 2x = m^2

Common Mistakes

Avoid these frequent errors
  • Incorrectly simplifying the ratio equation
    Don't just cross-multiply xBC=x2 \frac{x}{BC} = \sqrt{\frac{x}{2}} without careful algebra = wrong side length! Students often make errors when manipulating square roots. Always isolate BC step-by-step: multiply both sides by BC, then divide by the square root term.

Practice Quiz

Test your knowledge with interactive questions

Look at the rectangle below.

Side DC has a length of 1.5 cm and side AD has a length of 9.5 cm.

What is the perimeter of the rectangle?

1.51.51.5AAABBBCCCDDD9.5

FAQ

Everything you need to know about this question

How do I handle the square root in the ratio?

+

Start by writing the ratio as xBC=x2 \frac{x}{BC} = \frac{\sqrt{x}}{\sqrt{2}} . Then cross-multiply to get 2x=xBC \sqrt{2} \cdot x = \sqrt{x} \cdot BC , and solve for BC.

Why do we divide by square root x in the solution?

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We divide both sides by x \sqrt{x} to isolate BC. Remember: 2xx=2x \frac{\sqrt{2} \cdot x}{\sqrt{x}} = \sqrt{2} \cdot \sqrt{x} because x can be written as xx \sqrt{x} \cdot \sqrt{x} .

How does the Pythagorean theorem apply here?

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Since ABCD is a rectangle, triangle ABC is a right triangle. The diagonal AC is the hypotenuse, so we use: AB2+BC2=AC2 AB^2 + BC^2 = AC^2 or x2+(2x)2=m2 x^2 + (\sqrt{2x})^2 = m^2 .

What does (2x)2 (\sqrt{2x})^2 equal?

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When you square a square root, they cancel out! So (2x)2=2x (\sqrt{2x})^2 = 2x . This is why our final equation becomes x2+2x=m2 x^2 + 2x = m^2 .

Can I check my answer using specific values?

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Yes! Try x = 4: then BC=24=8=22 BC = \sqrt{2 \cdot 4} = \sqrt{8} = 2\sqrt{2} . Check the ratio: 422=2=42 \frac{4}{2\sqrt{2}} = \sqrt{2} = \sqrt{\frac{4}{2}}

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