<p>in the x y coordinate plane line m is the reflection of line L about the x-axis. if the slope of line m is -4/5, what is the slope of line L?</p>
<p>Collegeboard's answer :The slope of line m is -4/5 Therefore, if (x,y) is any point on line m then the point (x+5, y- 4) must also be on line m Since line m is the reflection of line L about the x--axis, the points (x, -y) and( x+5, - (y- 4) ) = (x+5, -y+4) are on line L Therefore, the slope of line L is given by ( -y+4-(-y) ) / x+5 - x which simplifies to 4/5.</p>
<p>I just don't understand the explanation. Why are the points (x, -y) and (x+5, -y+4) on line L?</p>