Q.Find the equations of the lines through the point $(-3, 4)$ that are parallel to the x-axis and to the y-axis.

A line parallel to the x-axis has the same y-coordinate, $b$, at every point, so its equation is simply $y=b$; it has slope $m=0$. A line parallel to the y-axis has the same x-coordinate, $a$, at every point, so its equation is $x=a$; it has an undefined slope, since the slope formula's denominator $x_2-x_1$ is always zero for two points on it. These are the two simplest possible equations of a line, read directly off the one fixed coordinate, and they are the only lines that cannot be produced by any of the slope-based forms — point-slope, two-point, slope-intercept, intercept — developed later in the chapter.