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Real and complex numbers
6 Class 9 Mathematics questions with answers and explanations.
Printable worksheet with answer key
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Which of these is an irrational number?
- 1 The square root of 2
- 2 4
- 3 3/4
- 4 0.5
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Correct answer: The square root of 2
The square root of 2 cannot be written as a ratio of two integers.
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What is i squared, where i is the imaginary unit?
- 1 0
- 2 -1
- 3 i
- 4 1
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What is (2 + 3i) + (4 - i)?
- 1 2 + 2i
- 2 8 + 3i
- 3 6 + 4i
- 4 6 + 2i
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Correct answer: 6 + 2i
Add real parts: 2 + 4 = 6. Add imaginary parts: 3 - 1 = 2.
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What is the conjugate of 3 + 4i?
- 1 -3 + 4i
- 2 3 - 4i
- 3 -3 - 4i
- 4 4 + 3i
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Correct answer: 3 - 4i
The conjugate changes the sign of the imaginary part.
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Which property is shown by a + b = b + a?
- 1 Commutative
- 2 Associative
- 3 Identity
- 4 Distributive
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Correct answer: Commutative
Changing the order of addition does not change the result: the commutative property.
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What is the additive identity of real numbers?
- 1 0
- 2 Infinity
- 3 -1
- 4 1