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Geometry Difficulty 3.5 AMC 10/12 Find the answer

Determine the range of slopes for line ll passing through point P(0,1)P(0, -1) such that ll does not intersect the line segment connecting points A(1,2)A(1, -2) and B(2,1)B(2, 1).

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

To determine the range of slopes for line ll that does not intersect with the line segment AB, we first need to calculate the slopes of line segments PA and PB.

The slope of PA, denoted as kPAk_{PA}, can be calculated using the formula for the slope between two points, m=y2y1x2x1m = \frac{y_2 - y_1}{x_2 - x_1}.
kPA=2(1)10=11=1 k_{PA} = \frac{-2 - (-1)}{1 - 0} = \frac{-1}{1} = -1

Similarly, for line segment PB:
kPB=1(1)20=22=1 k_{PB} = \frac{1 - (-1)}{2 - 0} = \frac{2}{2} = 1

Now, we know that the slopes of lines with a 135° inclination angle and a 45° inclination angle are 1-1 and 11, respectively.
Since the line ll should not intersect the line segment AB, its slope kk must satisfy k>kPBk > k_{PB} or k<kPAk < k_{PA}. This is because the slopes between these values would mean the line would intersect with segment AB at some point.

Therefore, the slope of line ll must be greater than 11 or less than 1-1, and as a result, the inclination angle range for line ll is between 45° and 135°, not inclusive.

(45°, 135°) \boxed{(\text{45°, 135°})}

Hence, the range of slopes for line ll is translated into the range of inclination angles as (45°,135°)(45°,135°).

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.