For what value of k given below is \(\frac{{{{\left( {k + 2} \right)}^2}}}{{k - 3}}\) an integer?
4, 8, 28
The problem asks us to find the set of values for k for which the given algebraic expression results in an integer.
The expression is given as:
$$ E(k) = \frac{{{{\left( {k + 2} \right)}^2}}}{{k - 3}} $$
To determine when this expression yields an integer, we can simplify it. Let's use a substitution to make the expression easier to handle. Let \( x = k - 3 \). This implies that \( k = x + 3 \).
Now, substitute \( k = x + 3 \) into the expression \( k + 2 \):
$$ k + 2 = (x + 3) + 2 = x + 5 $$
Substitute these back into the original expression \( E(k) \):
$$ E(k) = \frac{{(x + 5)^2}}{x} $$
Expand the numerator:
$$ E(k) = \frac{{x^2 + 2 \cdot x \cdot 5 + 5^2}}{x} = \frac{{x^2 + 10x + 25}}{x} $$
Now, divide each term in the numerator by \( x \):
$$ E(k) = \frac{{x^2}}{x} + \frac{{10x}}{x} + \frac{{25}}{x} = x + 10 + \frac{{25}}{x} $$
For \( E(k) \) to be an integer, the term \( \frac{{25}}{x} \) must also be an integer, since \( x \) (which is \( k - 3 \)) and \( 10 \) are integers (assuming \( k \) is an integer). This means that \( x \) must be a divisor of 25.
The divisors of 25 are the integers that divide 25 without leaving a remainder. These are:
\( \pm 1, \pm 5, \pm 25 \)
Now, we need to find the corresponding values of \( k \) using the relationship \( k = x + 3 \):
So, the possible integer values for \( k \) that make the expression an integer are \( \{4, 2, 8, -2, 28, -22\} \).
We need to find which of the given options contains only values from this set.
| Option | Values | Check Against Possible k | Result |
|---|---|---|---|
| 1 | {4, 8, 18} | 4 is possible, 8 is possible, 18 is not possible. | Incorrect |
| 2 | {4, 10, 16} | 4 is possible, 10 is not possible, 16 is not possible. | Incorrect |
| 3 | {4, 8, 28} | 4 is possible, 8 is possible, 28 is possible. | Correct |
| 4 | {8, 26, 28} | 8 is possible, 26 is not possible, 28 is possible. | Incorrect |
Let's verify the values in Option 3:
All values in Option 3 satisfy the condition.
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