Alan says that two lines in the coordinate plane are perpendicular if and only if the slopes of the lines are m and 1
m
. Identify and correct two errors in Alan's statement.

First, Alan should have said two
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lines rather than two lines because
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lines have undefined slope. Secondly, he should have had a
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sign on one of his expressions for the slope because the slopes of perpendicular lines have a product of
.