Using the triangle drawn against the line you can verify that the gradient is given by the difference in the y values divided by the difference in the x values. Looking at the line you can easily verify whether the gradient is positive or negative.
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Hidden Label: left parenthesis, "a" , "m" "a" plus "c" , right parenthesis Has graph. To audio trace, press ALT+T.a,ma+c
Label
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Hidden Label: left parenthesis, "b" , "m" "b" plus "c" , right parenthesis Has graph. To audio trace, press ALT+T.b,mb+c
Label
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Expression 11: "x" equals "b" left brace, "m" "a" plus "c" less than or equal to "y" less than or equal to "m" "b" plus "c" , right brace Has graph. To audio trace, press ALT+T.x=bma+c≤y≤mb+c
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Expression 12: "x" equals "b" left brace, "m" "b" plus "c" less than or equal to "y" less than or equal to "m" "a" plus "c" , right brace Has graph.x=bmb+c≤y≤ma+c
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Expression 13: "y" equals "m" "a" plus "c" left brace, "a" less than or equal to "x" less than or equal to "b" , right brace Has graph. To audio trace, press ALT+T.y=ma+ca≤x≤b