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Introduction to Slope


7.3: Calculate the Slope
  1. For each graph, record: vertical changehorizontal changeslopeABC
  2. Describe a procedure for finding the slope between any two points on a line.
  3. Write an expression for the slope of the line in the graph using the letters u,v,s, and t.
SummaryLet's say we have a glass cylinder filled with 50 ml of water and a bunch of marbles that are 3 ml in volume. If we drop marbles into the cylinder one at a time, we can watch the height of the water increase by the same amount, 3 ml, for each one added. This constant rate of change means there is a linear relationship between the number of marbles and the height of the water. Add one marble, the water height goes up 3 ml. Add 2 marbles, the water height goes up 6 ml. Add x marbles, the water height goes up 3x ml.Reasoning this way, we can calculate that the height, y, of the water for x marbles is y=3x+50. Any linear relationships can be expressed in the form y=mx+b using just the rate of change, m, and the initial amount, b. The 3 represents the rate of change, or slope of the graph, and the 50 represents the initial amount, or vertical intercept of the graph. We'll learn about some more ways to think about this equation in future lessons.Now what if we didn't have a description to use to figure out the slope and the vertical intercept? That's okay so long as we can find some points on the line! For the line graphed here, two of the points on the line are (3,3) and (9,5) and we can use these points to draw in a slope triangle as shown:The slope of this line is the quotient of the length of the vertical side of the slope triangle and the length of the horizontal side of the slope triangle. So the slope, m, is vertical changehorizontal change=26=13. We can also see from the graph that the vertical intercept, b, is 2. Putting these together, we can say that the equation for this line is y=13x+2.

Lina sees this problem. The points (2,-4), (x,y), A, and B all lie on the line. Find an equation relating x and y. What is the slope? How can you find the slope? What is the equation?

A you-pick blueberry farm offers 6 lbs of blueberries for $16.50.Sketch a graph of the relationship between cost and pounds of blueberries. MAKE A TABLE AND SLOPE.


Above, what is the slope?