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Given a sequence: 3, 7, 11, 15 Convert to a table X Y 1 2 3 4 3 7 11 15 Determine the common X difference and the common Y difference X Y 1 2 3 4 Rack ‘em by putting the y difference over the x difference 3 7 11 15 4 1 in this case 4 / 1 or 4 The equation begins y = mx + b We now have y = 4x + b To find the y-intercept we are looking for (0,b) So lets back up just one step in our sequence to X=0 X 0 1 2 3 4 Y 3 7 11 15 Then the Y can easily be determined as X Y 0 -1 1 3 2 7 3 11 4 15 This completes the equation that generates the sequence 3,7,11,15 Y = 4x + (-1) Or simply Y = 4x -1