Question 500020
x+y = 5
subtract x from both sides
y = -x +5 
This is the slope-intercept form.  It is useful for drawing graphs.
x=0, y = 5:  (0,5)
x=5, y = 0:  (5,0)
With two points you can draw a line.
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-x +y = 1
add x to both sides
y = x +1
x=0, y=1:  (0,1)
x=-1, y=0:  (-1,0)
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Note that the following graph will show where the lines cross.
That is the point that satisfies both equations simultaneously.
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{{{graph(500,500,-3,7,-3,7,-x+5,x+1)}}}