SOLVE EACH EQUATION

The variables x and y vary inversely. Use the given values to write an equation relating x and y. Then find y when x=3

1. x= 1, y=9

2. x= -3, y=8

3. x=7, y=2

4. x=3/4, y=28

5. x= -4, y = - 5/4

6. x= -12, y= - 1/6

1 answer

For inverse variation, we can express the relationship between \(x\) and \(y\) as:

\[ xy = k \]

where \(k\) is a constant. We will first find \(k\) using the given values of \(x\) and \(y\), and then we will use this constant to find \(y\) when \(x = 3\).

  1. For \(x = 1, y = 9\): \[ k = xy = 1 \cdot 9 = 9 \] The equation is \(xy = 9\).
    To find \(y\) when \(x = 3\): \[ 3y = 9 \quad \Rightarrow \quad y = \frac{9}{3} = 3 \]

  2. For \(x = -3, y = 8\): \[ k = xy = -3 \cdot 8 = -24 \] The equation is \(xy = -24\).
    To find \(y\) when \(x = 3\): \[ 3y = -24 \quad \Rightarrow \quad y = \frac{-24}{3} = -8 \]

  3. For \(x = 7, y = 2\): \[ k = xy = 7 \cdot 2 = 14 \] The equation is \(xy = 14\).
    To find \(y\) when \(x = 3\): \[ 3y = 14 \quad \Rightarrow \quad y = \frac{14}{3} \approx 4.67 \]

  4. For \(x = \frac{3}{4}, y = 28\): \[ k = xy = \frac{3}{4} \cdot 28 = 21 \] The equation is \(xy = 21\).
    To find \(y\) when \(x = 3\): \[ 3y = 21 \quad \Rightarrow \quad y = \frac{21}{3} = 7 \]

  5. For \(x = -4, y = -\frac{5}{4}\): \[ k = xy = -4 \cdot -\frac{5}{4} = 5 \] The equation is \(xy = 5\).
    To find \(y\) when \(x = 3\): \[ 3y = 5 \quad \Rightarrow \quad y = \frac{5}{3} \approx 1.67 \]

  6. For \(x = -12, y = -\frac{1}{6}\): \[ k = xy = -12 \cdot -\frac{1}{6} = 2 \] The equation is \(xy = 2\).
    To find \(y\) when \(x = 3\): \[ 3y = 2 \quad \Rightarrow \quad y = \frac{2}{3} \approx 0.67 \]

Summary of results when \(x = 3\):

  1. \( y = 3 \)
  2. \( y = -8 \)
  3. \( y \approx 4.67 \)
  4. \( y = 7 \)
  5. \( y \approx 1.67 \)
  6. \( y \approx 0.67 \)