Notes 9-3
Parallel Lines in the Coordinate Plane
Theorem 9.10a- If two non-vertical lines in the same plane are parallel, then they have
the same slope.
Theorem 9.10b- If the slopes of two non-vertical lines in the coordinate plane are
equal, then the lines are parallel.
Ex. 1: The vertices of quadrilateral ABCD are A(2, -4), B(6, -2), C(2,6), and D(-1,2).
a. Show that two sides of the quadrilateral are parallel.
b. Show that the quadrilateral has two right angles.
Ex. 2 Write the equation for l 1 the line through (-2,5) that is parallel to the line
l2 whose equation is 2x+y=7.
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Ex. 3: For the following pairs of lines, tell whether the lines are parallel,
perpendicular, or neither.
a. x + y = 7
b. x - y = 3
Ex. 4: Quadrilateral ABCD has two pairs of parallel sides,
A(1,2), B(7,-1), and C(8,2) are the coordinates of three of
the vertices.
a.
b.
c.
d.
e.
f.
g.
What is the slope of
What is the slope of
Write the equation for
What is the slope of
What is the slope of
Write an equation for
Use the equation of
and the equation of
coordinates of D.
to find the
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