In this question, we have to find an equation for two lines, depending on the input x, which creates the following piecewise function for this graph:
[tex]y = t, 0 \leq t \leq 10, -t + 20, 10 \leq t \leq 20[/tex]
Equation of a line:
The equation of a line is given by:
[tex]y = mt + b[/tex]
In which m is the slope and b is the y-intercept(value of y when x = 0).
This situation:
x between 0 and 10:
From here, we can take two points (t,y). I will take (0,0) and (10,10).
From point (0,0), we get that when [tex]x = 0, y = 0[/tex], which means that the y-intercept is [tex]b = 0[/tex], thus:
[tex]y_1 = mt[/tex]
To find the slope, when we have two points, it is given by change in y divided by change in t, so:
Change in t: 10 - 0 = 10
Change in y: 10 - 0 = 10
Slope: [tex]m = \frac{10}{10} = 1[/tex]
Thus, the first definition is:
[tex]y_1 = t, 0 \leq t < 10[/tex]
x between 10 and 20:
I will take the points (10,10) and (20,0).
First, we find the slope:
Change in t: 20 - 10 = 10
Change in y: 0 - 10 = -10
Slope: [tex]m = \frac{-10}{10} = -1[/tex]
Thus:
[tex]y_2 = -t + b[/tex]
For the intercept, we have point (20,0), which means that when [tex]t = 20, y = 0[/tex]. So
[tex]0 = -20 + b[/tex]
[tex]b = 20[/tex]
Thus, the second definition is:
[tex]y_2 = -t + 20, 10 \leq t \leq 20[/tex]
Write an equation for the graph.
We use the two definitions, that is:
[tex]y = y_1, 0 \leq t \leq 10, y_2, 10 \leq t \leq 20[/tex]
So
[tex]y = t, 0 \leq t \leq 10, -t + 20, 10 \leq t \leq 20[/tex]
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