Question 982527
It has a slope of 1 and a y-intercept of {{{a}}}. 
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{{{graph(300,300,-10,10,-10,10,x,x+3,x-7,x+9)}}}
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Here's the graph with 4 values of {{{a}}}.
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Red : {{{a=0}}}
Green : {{{a=3}}}
Blue : {{{a=-7}}}
Purple : {{{a=9}}}