Here's the problem:

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**Problem:** Recall that you can use two points on a line to determine an equation for the line. Suppose two points in a coordinate plane have coordinates *(x1, y1)* and *(x2, y2)*.

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**A.** Write a formula that gives the slope *b* of the line containing the two points.

Alright, I know this is $\displaystyle b = \frac{y1-y2}{x1-x2}$. No problem there.

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**B. **Solve the equation for in Part a for *y1* in terms of the other variables.

I don't quite remember how to do this. In the end, I got $\displaystyle Y1 = b(x1-x2)+y2$ Please correct me on this.

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**C. **In your equation from Part b, replace the point with coordinates *(x1, y1)*, with a general point *(x, y)* on the line. Explain how this equation is now that of a line with slope *b* through the point *(x2, y2).*

This is the part I thought was a brain teaser/tongue twister. What do you do here?

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**D.** Use your equation from Part c to write the equation of the line that contains the points *(8, 12)* and has slope *-2*. What is the y-intercept of this line?

I don't have the equation for C. yet, so I'll wait for help on that first. :)