004 Sample Final A, Problem 14

 a) Find an equation of the line passing through (-4, 2) and (3, 6).

 b) Find the slope of any line perpendicular to your answer from a)

Foundations
1) How do you find the slope of a line through points $(x_{1},y_{1})$ and $(x_{2},y_{2})$?
2) What is the equation of a line?
3) How do you find the slope of a line perpendicular to a line $y$?
Answer:
1) The slope is given by $m={\frac {y_{2}-y_{1}}{x_{2}-x_{1}}}$.
2) The equation of a line is $y-y_{1}=m(x-x_{1})$ where $(x_{1},y_{1})$ is a point on the line.
3) The slope is given by $-{\frac {1}{m}}$ where $m$ is the slope of the line $y$.

Solution:

Step 1:
Using the above equation, the slope is equal to $m={\frac {6-2}{3-(-4)}}={\frac {4}{7}}$.

Step 2:
The equation of the line is $y-6={\frac {4}{7}}(x-3)$. Solving for $y$,
we get $y={\frac {4}{7}}x+{\frac {30}{7}}$.

Step 3:
The slope of any line perpendicular to the line in Step 2 is $-{\frac {1}{({\frac {4}{7}})}}=-{\frac {7}{4}}$.

Final Answer:
The slope is ${\frac {4}{7}}$, the equation of the line is $y={\frac {4}{7}}x+{\frac {30}{7}}$, and
the slope of any line perpendicular to this line is $-{\frac {7}{4}}$.

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