COPYRIGHT NOTICE
Copyright 2007 Samuel Dagan
dagan@post.tau.ac.il
/general/copyright.xhtml
Straight line
Slope and intersection of lines
The origin of the figure is at (0,0)
© Samuel Dagan
Straight line
-3
-2
-1
1
2
3
-3
-2
-1
1
2
3
x
y
y=k1x+b1
b1
x1
x2
y1
y2
Δx
Δy
α1
α1
y=k2x+b2
α2
b2
α1
α2
α2−α1
Click to reveal!
y = −2x/3 + 2
The straight line y = k1x+b1 is
plotted in a coordinate sytem
with identical scales of the
axes.
For x=0 one obtains y = b1
= −3 ,
which is called the y-intercept.
Two points: (x1,y1) and (x2,
y2) will
be chosen from this line next,
and the two increments
Δx=x2−x1
with Δy=y2−y1 will be plotted.
From the above
expression of
the line, it follows that
k1=Δy/Δx .
But k1=tanα1 , and α1 is also the
angle of the line with the x axis.
Note that in this
particular case
k1=2 and
the line is: y=2x−3 .
Another line will be plotted
next.
b2 and α2 will be marked next.
One of
the two angles between
the lines
is α2−α1, as shown next.
What is the equation of
the second straight line?
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