Question 537572
The x-axis is horizontal and the y-axis is vertical
When you have an equation {{{ y = f(x) }}}, like {{{ y = 2x + 1 }}},
think of it as passing though the points
(x1,y1), (x2,y2), (x3,y3), (x4,y4) . . . etc.
For any of these points, if I know x I can find y
If I know y, I can find x.
Suppose (x1,y1) = (22,y1)
Just replace x with 22, and you find y1:
{{{ y1 = 2*22 + 1 }}}
{{{ y1 = 45 }}}, so the point is (22,45)
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Two special points are (0,y1) and (x1,0)
These are called intercepts because they lie on the 
vertical and horizontal axes
If I have (0,y1), I can find y1
{{{ y1 = 2*0 + 1 }}}
{{{ y1 = 1 }}}, so the point is (0,1)
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You can turn the problem around and say
" Does the point (9,11) lie on this equation?"
To find out:
{{{ y = 2x + 1 }}}
{{{ 11  = 2*9 + 1 }}}
{{{ 11 = 19 }}}
This means the point does not lie on the equation
Does the point (43, 87) lie on the equation?
{{{ 87 = 2*43 + 1 }}}
{{{ 87 = 86 + 1 }}}
{{{ 87 = 87 }}}
Yes, this point is on the equation
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All you need is 2 points to plot a straight line, but
you can find as many points as you want, and they 
will all lie on the line.
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I doesn't matter how the equation is written, you
just need x's and y's
Suppose I have
{{{ 3*( x + 1) - 4y = 2x }}}
I have (3,y1). What is y1?
{{{ 3*( 3 + 1 ) - 4y = 2*3 }}}
{{{ 3*4 - 4y = 6 }}}
{{{ -4y = 6 - 12 }}}
{{{ -4y = -8 }}}
{{{ y = 2 }}}, so my point is (3,2)
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Hope this helps