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Timothy evaluated the expression using \( x = 3 \) and \( y = -4 \).

[tex]\[
\frac{x y^{-2}}{3 x^2 y^{-4}}
\][/tex]

1. \(\left(\frac{1}{3}\right) x^{-1} y^2\)

2. \(\left(\frac{1}{3}\right) 3^{-1} (-4)^2\)

3. \(\left(\frac{1}{3}\right) \left(\frac{1}{3^1}\right) (-4)^2\)

4. \(\left(\frac{1}{3}\right) \left(\frac{1}{3}\right) (-16)\)

5. \( 5 - \frac{16}{9} \)

6. [tex]\( 5 - \frac{16}{9} \)[/tex]

Sagot :

Certainly! Let's solve the given expression step-by-step using the given values \( x = 3 \) and \( y = -4 \).

The expression given is:
[tex]\[ \frac{x y^{-2}}{3 x^2 y^{-4}} \][/tex]

### Step-by-Step Solution:
1. Simplify the expression:
[tex]\[ \frac{x y^{-2}}{3 x^2 y^{-4}} \][/tex]
Using properties of exponents: \( y^{-a} = \frac{1}{y^a} \), we can rewrite the expression.

2. Combine the exponents:
[tex]\[ = \frac{x y^{-2}}{3 x^2 \cdot y^{-4}} = \frac{x \cdot \frac{1}{y^2}}{3 x^2 \cdot \frac{1}{y^4}} = \frac{x \cdot \frac{1}{y^2}}{3 x^2 \cdot \frac{1}{y^4}} = \frac{x}{y^2} \cdot \frac{y^4}{3 x^2} = \frac{x \cdot y^4}{y^2 \cdot 3 x^2} \][/tex]

3. Simplify further by canceling out common terms:
[tex]\[ = \frac{x \cdot y^4}{3 x^2 \cdot y^2} = \frac{x \cdot y^2 \cdot y^2}{3 x^2 \cdot y^2} = \frac{x \cdot y^2}{3 x^2} = \frac{y^2}{3 x} \][/tex]
So the expression simplifies to:
[tex]\[ \frac{1}{3} \cdot x^{-1} \cdot y^2 \][/tex]

4. Substitute the given values \( x = 3 \) and \( y = -4 \):
[tex]\[ \left( \frac{1}{3} \right) \cdot 3^{-1} \cdot (-4)^2 \][/tex]

5. Evaluate the individual terms:
[tex]\[ = \left( \frac{1}{3} \right) \cdot \left( \frac{1}{3} \right) \cdot 16 \][/tex]
Since \(3^{-1} =\frac{1}{3}\) and \( (-4)^2 = 16 \)

6. Multiply them together:
[tex]\[ = \left( \frac{1}{3} \right) \cdot \left( \frac{1}{3} \right) \cdot 16 = \left( \frac{1}{3} \right) \cdot \left( \frac{16}{3} \right) = \frac{16}{9} \][/tex]

Thus, the final evaluated result is:
[tex]\[ \frac{16}{9} \approx 1.7777777777777777 \][/tex]