# a question on “basic triangle at q”

Could someonehelp me to understand these sentences:

A “basic triangle at $q$” will mean a triangle which has the sides adjacent to the vertex $q$ of equal length and an angle at $q$ of measure $30$. The height (or bisector) at $q$ will be used to orient the triangle vertically or with slope $-1$.

A basic triangle at $q$ is an isosceles triangle with one vertex at the point $q$. Two equal sides of the triangle form the angle at $q$, and that angle is a 30 degree angle. If you draw a perpendicular from the point $q$ to the opposite side of the triangle, thereby bisecting the angle at vertex $q$, this perpendicular either is vertical or has a slope of $-1$, meaning that it runs diagonally from upper left to lower right at a 45 degree angle to the horizontal. Here's a not-very-good picture: