You may need to determine the yintercept of a trend line in order to understand more about the data that the trend line is representing. A trend line is a line that is drawn above, below or through various data points in order to show their general direction. The trend line may be drawn from the upper left corner to the lower right corner, indicating that the data have a negative slope, or from the lower left corner to the upper right corner, indicating that the data have a positive slope. The yintercept of the trend line is the point at which the trend line has an x value of zero.
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Examine the trend line that is on the graph. One of the methods for determining the yintercept is through observation. Find the xaxis, or horizontal axis on the graph, and locate the value at which x=0. Place your pencil over this point. Follow the vertical line above this point with your pencil until the pencil intersects the trend line. Look at the yaxis, or vertical axis, and find the value for which this intersection occurs. This value is the yintercept.

Compare the general equation of a line to the equation of the trend line. The general formula for a line is y=mx+b, for which m is the slope, b is the yintercept, x is any x value and y is any y value. By looking at the equation of the trend line, you can determine the yintercept. For example, if the equation of the trend line is y=2x+5, the yintercept is 5. You would receive this same answer if you let x=0.

Review the pointslope formula. If the trend line does not have an equation, then you will want to create one in order to determine the yintercept. The pointslope formula is (yy1)=m(xx1), where m is the slope, y1 is the y coordinate and x1 is the x coordinate.

Find the slope of the line. In order to generate the equation of the line, you need to find the slope. The equation of the slope is m=(y2y1)/(x2x1), where x1 and y1 are one set of coordinates on the trend line and x2 and y2 are another set of coordinates on the trend line. For example, two points on the trend line may be (2,9) and (3,11). Putting these points into the equation, you get m=(119)/(32). You should calculate an answer of m=2.

Find another point on the trend line and put the values of the point and the slope into the pointslope formula. For example, if the point is (1,7) and the slope is m=2, you get (y7)=2(x1). Solving for y, you receive the equation y=2x+5. Therefore, the yintercept of the trend line is 5.
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