The expression 7•3x is not equal to the expression 21x. You might think that the two expressions are the same since 7x3 is 21 but the first expression is a dot product. This kind of expression includes the magnitude and direction of the vector in an expression, for example, <span>7•3x. The second expression, 21x, expresses only the magnitude and does not include the direction.</span>
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Let the set of all Odd multiples of 9 between 2 and 82 be denoted by D, then, using set-builder notation,

The odd multiples of 9,
, in the range
form the set

Each member of the set is a term of the arithmetic progression

where the values of
range from 0 to 4, or 
Putting these facts together, we get the result

Learn more about set-builder notation here: brainly.com/question/17238769