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Subjects
Class 10MathematicsReal NumbersProof of irrationality of √2, √3, √5HardLevel 18
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In the proof for (\sqrt{5}), if (a=5k), what is proved about (b)?

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Answer and explanation

Correct answer: (b) is divisible by (5)

Step 1: In (a^2=5b^2), putting (a=5k) gives (25k^2=5b^2). Step 2: Simplifying gives (b^2=5k^2), so (5\mid b^2) and (5\mid b). Step 3: This is the final step against coprimality.

Related tags

Real-NumbersRoot5SubstitutionContradictionHard

Frequently asked questions

What is the correct answer to this question?

(b) is divisible by (5)

Why is this the correct answer?

Step 1: In (a^2=5b^2), putting (a=5k) gives (25k^2=5b^2). Step 2: Simplifying gives (b^2=5k^2), so (5\mid b^2) and (5\mid b). Step 3: This is the final step against coprimality.

Which subject and chapter does this question cover?

This is a Class 10 Mathematics question. Chapter: Real Numbers. Topic: Proof of irrationality of √2, √3, √5.

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10 more MCQs
  1. 1Which assumption is taken first to prove that (\sqrt{2}) is irrational?
  2. 2If (\sqrt{2}=\frac{p}{q}), what is obtained after squaring both sides?
  3. 3From the equation (p^2=2q^2), what do we learn about (p^2)?
  4. 4If (p^2) is even, which conclusion about (p) is correct?
  5. 5If (p) is even, in which form can (p) be written?
  6. 6What conclusion is obtained by putting (p=2k) in (p^2=2q^2)?
  7. 7What is the final contradiction in the proof of (\sqrt{2})?
  8. 8What is the correct final conclusion of the proof of (\sqrt{2})?
  9. 9If (\sqrt{3}) is assumed rational, in which form is it written?
  10. 10If (\sqrt{3}=\frac{p}{q}), which equation is obtained after squaring?
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