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Given that is irrational, prove that is irrational. Which statement correctly justifies the conclusion?

Class 10Real NumbersNumber Systems
  • AA non-zero rational times an irrational is irrational, and a rational subtracted from an irrational stays irrational.
  • BThe product of two irrationals is always irrational.
  • CEvery surd is irrational, so no proof is needed.
  • D is rational because 3 is rational.

Step-by-Step Solution

is (non-zero rational 2) × (irrational ) = irrational. Subtracting the rational 3 keeps it irrational. Hence is irrational.
Answer: A) A non-zero rational times an irrational is irrational, and a rational subtracted from an irrational stays irrational.

Key idea: Sum/product of rational and irrational

**Useful results**:

1. The sum or difference of a rational and an irrational is IRRATIONAL.
Proof: if (rational + irrational) = rational, then irrational = rational − rational = rational. Contradiction.

2. The product of a NON-ZERO rational and an irrational is IRRATIONAL.

3. The sum/product of two irrationals can be RATIONAL or IRRATIONAL.
Example: (irrational); (rational).
Example: (rational); (irrational).

These are the rules you cite when proving expressions like ' is irrational'.

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