Because the transverse line passing through the two axes, meets with two different lines. On the positive X-axis, one end of the line passed through it, meeting at the point, +6, i.e considering your reading from zero on the positive X-axis, which therefore makes it 6x. The second end of the line met the point, +3, on the positive Y-axis. So when writing the equation for the transverse line or the line <em>l</em>,...
