To find the equation of a line in slope-intercept form \( y = mx + b \), where \( m \) is the slope and \( b \) is the y-intercept, we can use the slope (-1/2) and the point (1, 2).
We have:
- \( m = -\frac{1}{2} \)
- The point \( (x_1, y_1) = (1, 2) \)
First, we can substitute the slope and the coordinates of the point into the equation \( y = mx + b \):
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Start with \( y = mx + b \): \[ y = -\frac{1}{2}x + b \]
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Substitute the coordinates of the point \( (1, 2) \): \[ 2 = -\frac{1}{2}(1) + b \] \[ 2 = -\frac{1}{2} + b \]
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To isolate \( b \), add \( \frac{1}{2} \) to both sides: \[ 2 + \frac{1}{2} = b \] \[ b = \frac{4}{2} + \frac{1}{2} = \frac{5}{2} \]
Now convert \( \frac{5}{2} \) to a decimal: \[ \frac{5}{2} = 2.5 \]
Thus, the y-intercept \( b \) is \( 2.5 \).
So the y-intercept of this line, rounded to the nearest tenth, is \( \boxed{2.5} \).