Skin tags that have changed color or bleed may require your doctor's evaluation and reassurance. Rarely, thrombosed skin tags may be a sign of another condition and need to be biopsied.
The x-axis and y-axis are two lines that create the coordinate plane. The x-axis is a horizontal line and the y-axis is a vertical line. I'm sure you've heard that a million times, but it might hard for you to remember which one is which. Here is a little trick to help you remember...
a) Through any point P in the plane, there is one and only one vertical line within the plane and one and only one horizontal line within the plane. This symmetry breaks down as one moves to the three-dimensional case. b) A vertical line is any line parallel to the vertical direction.