# Using Equations for Lines

After interacting with the applet below for a minute or two, answer the question that follows.

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Writing Equations of Lines.

• Enter the equation of the line in the applet below and click “Check”. ​
• Click “New Line” to continue.​

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Draw the Dilation of a Triangle.

Here in the applet below is triangle ABC.

(1). Draw the dilation of triangle ABC with center (0,1) and scale factor 2.

(2). Draw the dilation of triangle ABC with center (0,1) and scale factor 2.5.

(3). Where is C mapped by the dilation with center (0, 1) and scale factor s ?

(4). For which scale factor does the dilation with center (0, 1) send C to (9, 5.5) ?

(5). Explain how you know.

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Finding the Equation of a Line

Here in the applet below is a line.

(1). Using what you know about similar triangles, find an equation for the line in the diagram. (You can use the applet above to help).

(2). What is the slope of this line? Does it appear in your equation?

There are many different ways to write down an equation for a line like the one in the problem.

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All three points displayed are on the line.

Find an equation relating x and y.

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A dilation with scale factor 2 sends A to B. Where is the center of the dilation?

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