Q. 165.0( 1 Vote )

Mark the tick against the correct answer in the following:Let Q be the set of all rational numbers, and * be the binary operation, defined by a * b = a + 2b, thenA. * is commutative but not associativeB. * is associative but not commutativeC. * is neither commutative nor associativeD. * is both commutative and associative

According to the question ,

Q is set of all rarional numbers

R = {(a, b) : a * b = a + 2b }

Formula

* is commutative if a * b = b * a

* is associative if (a * b) * c = a * (b * c)

Check for commutative

Consider , a * b = a + 2b

And , b * a = b + 2a

Both equations will not always be true .

Therefore , * is not commutative ……. (1)

Check for associative

Consider , (a * b) * c = (a + 2b) * c = a+2b + 2c

And , a * (b * c) = a * (b+2c) = a+2(b+2c) = a+2b+4c

Both the equation are not the same and therefore will not always be true.

Therefore , * is not associative ……. (2)

Now , according to the equations (1) , (2)

Correct option will be (C)

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