Triangles

only in an isosceles triangle the vertex opposite to the base is the MAIN vertex. and the base in an isosceles triangle is the common side to the equal angles.

nature of triangle: type of triangle (isosceles,equilateral,right triangle)

Semi equilateral triangle: a triangle with one 90 degrees angle and one 30 degrees angle and one 60 degrees angle so this is also considered another nature of triangles.

symmetrical is when they r like a MIRROR to each other (equal,same,identical…)

in a symmetry whatever is after with respect is the mirror or is in the middle

substitution: means to find out from the equal ones: ex: given, RS=RU, RU=RT, sooo RS=RT by substitution

main vertex: principal vertex