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3. A linear equation in the [tex]$xy$[/tex]-plane intercepts the [tex]$y$[/tex]-axis at -3. For every 2 units the [tex][tex]$y$[/tex][/tex]-coordinate of the line increases, the [tex]$x$[/tex]-coordinate decreases by 7 units. Which of the following is the correct equation for this line?

(A) [tex]y = \frac{7}{2} x + 3[/tex]
(B) [tex]y = \frac{2}{7} x - 3[/tex]
(C) [tex]y = -\frac{2}{7} x - 3[/tex]
(D) [tex]y = \frac{3}{2} x - 7[/tex]


Sagot :

Let's find the equation of the line given the information provided:

1. Identify the y-intercept:
- The line intercepts the [tex]\( y \)[/tex]-axis at [tex]\(-3\)[/tex]. This means that the [tex]\( y \)[/tex]-intercept ([tex]\( b \)[/tex]) is [tex]\(-3\)[/tex].

2. Determine the slope:
- We know that for every 2 units increase in the [tex]\( y \)[/tex]-coordinate, the [tex]\( x \)[/tex]-coordinate decreases by 7 units.
- The slope ([tex]\( m \)[/tex]) of the line is the change in [tex]\( y \)[/tex] divided by the change in [tex]\( x \)[/tex]. Here, the change in [tex]\( y \)[/tex] ([tex]\( \Delta y \)[/tex]) is 2, and the change in [tex]\( x \)[/tex] ([tex]\( \Delta x \)[/tex]) is -7. Thus, the slope [tex]\( m \)[/tex] is calculated as follows:
[tex]\[ m = \frac{\Delta y}{\Delta x} = \frac{2}{-7} = -\frac{2}{7} \][/tex]

3. Write the equation of the line:
- The general form of the equation of a line is:
[tex]\[ y = mx + b \][/tex]
- Substituting the slope [tex]\( m \)[/tex] and the y-intercept [tex]\( b \)[/tex] into the equation:
[tex]\[ y = -\frac{2}{7}x - 3 \][/tex]

Therefore, the correct equation for this line is:
[tex]\[ \boxed{y = -\frac{2}{7} x - 3} \][/tex]

So, the correct answer choice is:
[tex]\[ \text{(C) } y = -\frac{2}{7} x - 3 \][/tex]