Writing an Equation to Represent a Real-World Problem

Caitlin is designing a railing for a set of stairs. The railing will begin at a height of 36 inches and follow the slant of the stairs, which decreases 9 inches for every 12 horizontal inches.

Which function can represent the height, [tex]\( y \)[/tex], of the railing in inches according to the horizontal distance in inches, [tex]\( x \)[/tex], from the top of the stairs?

A. [tex]\( y = -\frac{3}{4}x + 36 \)[/tex]

B. [tex]\( y = -3x + 36 \)[/tex]

C. [tex]\( y = \frac{3}{4}x + 36 \)[/tex]

D. [tex]\( y = 3x + 36 \)[/tex]



Answer :

To determine the correct function that represents the height [tex]\( y \)[/tex] of the railing in inches according to the horizontal distance [tex]\( x \)[/tex] in inches from the top of the stairs, follow these steps:

### Step-by-Step Solution

1. Identify Key Pieces of Information:
- The railing starts at a height of 36 inches.
- The height decreases by 9 inches for every 12 horizontal inches.

2. Determine the Slope:
- The slope [tex]\( m \)[/tex] of a line is given by the change in vertical distance divided by the change in horizontal distance.
- Here, the vertical decrease is 9 inches and the horizontal distance is 12 inches.
[tex]\[ m = \frac{\text{change in height}}{\text{horizontal distance}} = \frac{-9}{12} = -\frac{3}{4} \][/tex]
- The negative sign indicates that the height is decreasing as you move horizontally.

3. Identify the Y-Intercept:
- The y-intercept ([tex]\( b \)[/tex]) is the initial height of the railing when [tex]\( x = 0 \)[/tex].
- In this problem, the railing starts at a height of 36 inches, so [tex]\( b = 36 \)[/tex].

4. Construct the Function:
- Using the slope-intercept form of a linear equation [tex]\( y = mx + b \)[/tex], where [tex]\( m \)[/tex] is the slope and [tex]\( b \)[/tex] is the y-intercept:
[tex]\[ y = -\frac{3}{4}x + 36 \][/tex]

5. Verify the Options:
- Now, let's check which of the given options corresponds to this function:
- [tex]\( y = -\frac{3}{4} x + 36 \)[/tex]
- [tex]\( y = -3 x + 36 \)[/tex]
- [tex]\( y = \frac{3}{4} x + 36 \)[/tex]
- [tex]\( y = 3 x + 36 \)[/tex]

The correct function that represents the height [tex]\( y \)[/tex] of the railing in inches according to the horizontal distance [tex]\( x \)[/tex] is:
[tex]\[ y = -\frac{3}{4} x + 36 \][/tex]

### Conclusion

Therefore, the correct function to represent the height of the railing is:
[tex]\[ y = -\frac{3}{4} x + 36 \][/tex]

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