This is a free lesson from our course in Algebra I
In this lesson, you'll learn how to determine if two lines are parallel. Parallel lines are lines in the same plane that never meet no matter how far they run.
Two words in that statement that seem to confuse many people are plane and parallel.
Let's look at these terms in a practical sense.
• a plane is a flat surface that has length and width, but no thickness.
• surface is defined as the exterior of an object. Surface has length and width. You can see it or imagine it,
but because it has no thickness, you can't hold on to it.(More text below video...)
(Continued from above) The parallel symbol is  .
For example, AB  CD indicates that line AB is parallel to line CD. Parallel lines
have the same slope. If two lines y_{1} = m_{1}x_{1}
+ c and y_{2} = m_{2}x_{2} + c are parallel,
then m_{1} = m_{2} because m_{1} and m_{2} represent
the slopes of the two lines. For example, 6y = 3x + 30 and 2y
= x + 4 are parallel lines with slope of 1/2.
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