Consider the operators โ—Š and โ–ก defined by ๐‘Ž โ—Š ๐‘ = ๐‘Ž + 2๐‘, ๐‘Žโ–ก๐‘ = ๐‘Ž๐‘,โ€ฆ

2024

Consider the operators โ—Š and โ–ก defined by ๐‘Ž โ—Š ๐‘ = ๐‘Ž + 2๐‘, ๐‘Žโ–ก๐‘ = ๐‘Ž๐‘, for positive integers. Which of the following statements is/are TRUE?

  1. A.

    Operator โ—Š obeys the associative law

  2. B.

    Operator โ–ก obeys the associative law

  3. C.

    Operator โ—Š over the operator โ–ก obeys the distributive law

  4. D.

    Operator โ–ก over the operator โ—Š obeys the distributive law

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Correct answer: B, D

Correct statements and why:

  • Operator โ–ก obeys the associative law: (a โ–ก b) โ–ก c = (ab)c = a(bc) = a โ–ก (b โ–ก c).

  • Operator โ–ก over the operator โ—Š obeys the distributive law: a โ–ก (b โ—Š c) = a(b + 2c) = ab + 2ac, and (a โ–ก b) โ—Š (a โ–ก c) = (ab) โ—Š (ac) = ab + 2ac, so they are equal.

Why the other statements are false:

  • Operator โ—Š is not associative: (a โ—Š b) โ—Š c = a + 2b + 2c, while a โ—Š (b โ—Š c) = a + 2b + 4c, so they differ in general. Example: with a = b = c = 1, (1 โ—Š 1) โ—Š 1 = 5 but 1 โ—Š (1 โ—Š 1) = 7.

  • โ—Š does not distribute over โ–ก: a โ—Š (b โ–ก c) = a + 2(bc) whereas (a โ—Š b) โ–ก (a โ—Š c) = (a + 2b)(a + 2c), which are not equal in general. Example: a = b = c = 1 gives 3 on the left and 9 on the right.

Final answer: The true statements are those asserting that multiplication (โ–ก) is associative and that multiplication distributes over โ—Š.

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