Equations Of Lines Curve Fitting Page 2

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III. Special Lines that are Vertical and Horizontal (p. 229)
*When writing the equation of a vertical line or horizontal line, plot the point on the line, then
“stretch out” the point so that it is a vertical (up and down) or a horizontal line (across).
The equation of the vertical line is x = the value on the x-axis that the stretched line hit.
The equation of the horizontal line is y = the value on the y-axis that the stretched line hit.
Ex. Write the equation of the vertical line that passes through (1, 4).
*Plot the point, then stretch it out vertically. The graph hits the x-axis
at 1, so the equation of the vertical line is ___________.
Ex. Write the equation of the horizontal line that passes through (1, -3).
*Plot the point, then stretch it out horizontally. The graph hits the
y-axis at –3, so the equation of the horizontal line is ___________.
In general, for a vertical line that contains ( a, b ), the equation is x = a.
and for a horizontal line that contains ( a , b), the equation is y = b.
IV. Equations of Parallel and Perpendicular Lines (pp. 229 – 231)
Parallel lines have the same slopes and different y-intercepts.
Perpendicular lines have slopes that have a product of –1 or negative (opposite) reciprocals.
Ex. Find the equation in standard form of the line through (-2, 4) which is parallel to 3 x + 8 y = 7.
*First find the slope of the given line, then borrow it as is.
Ex. Find the equation in standard form of the line through (-2, 4) which is perpendicular
to 3 x +8 y = 7.
*Find the slope of the given line, then use the opposite reciprocal to write the equation of your line.

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