13. The table shows a set of values for [tex]\( x \)[/tex] and [tex]\( y \)[/tex]:

[tex]\[
\begin{array}{c|c}
x & y \\
\hline
1 & 9 \\
2 & 2 \frac{1}{4} \\
3 & 1 \\
\end{array}
\][/tex]

[tex]\( y \)[/tex] is inversely proportional to the square of [tex]\( x \)[/tex].

(a) Find an equation for [tex]\( y \)[/tex] in terms of [tex]\( x \)[/tex].



Answer :

To find an equation for [tex]\( y \)[/tex] in terms of [tex]\( x \)[/tex] when [tex]\( y \)[/tex] is inversely proportional to the square of [tex]\( x \)[/tex], we can start by expressing the relationship mathematically:

[tex]\[ y \propto \frac{1}{x^2} \][/tex]

This can be rewritten as:

[tex]\[ y = \frac{k}{x^2} \][/tex]

where [tex]\( k \)[/tex] is a constant.

To determine the value of [tex]\( k \)[/tex], we use the given pairs of values for [tex]\( x \)[/tex] and [tex]\( y \)[/tex] in the table.

From the table:
[tex]\[ \begin{array}{|c|c|} \hline x & y \\ \hline 1 & 2.25 \\ 2 & 1 \\ 3 & 0.25 \\ 9 & 0.027777777777777776 \\ \hline \end{array} \][/tex]

We'll start with the first pair [tex]\((x, y) = (1, 2.25)\)[/tex]:

[tex]\[ y = \frac{k}{x^2} \][/tex]

By substituting [tex]\( x = 1 \)[/tex] and [tex]\( y = 2.25 \)[/tex] into the equation, we find [tex]\( k \)[/tex]:

[tex]\[ 2.25 = \frac{k}{1^2} \][/tex]
[tex]\[ k = 2.25 \][/tex]

Now that we have [tex]\( k = 2.25 \)[/tex], we can write the equation for [tex]\( y \)[/tex] in terms of [tex]\( x \)[/tex] as follows:

[tex]\[ y = \frac{2.25}{x^2} \][/tex]

Let's verify this equation with the other values in the table:

1. For [tex]\( x = 2 \)[/tex]:
[tex]\[ y = \frac{2.25}{2^2} = \frac{2.25}{4} = 0.5625 \][/tex]

2. For [tex]\( x = 3 \)[/tex]:
[tex]\[ y = \frac{2.25}{3^2} = \frac{2.25}{9} = 0.25 \][/tex]

3. For [tex]\( x = 9 \)[/tex]:
[tex]\[ y = \frac{2.25}{9^2} = \frac{2.25}{81} = 0.027777777777777776 \][/tex]

These values confirm that our equation [tex]\( y = \frac{2.25}{x^2} \)[/tex] is correct for the given pairs of [tex]\( x \)[/tex] and [tex]\( y \)[/tex].

Therefore, the equation for [tex]\( y \)[/tex] in terms of [tex]\( x \)[/tex] is:

[tex]\[ y = \frac{2.25}{x^2} \][/tex]