For fabric at least 10 cm wider than half the chest measurement, 2 lengths + 1 sleeve length + 100 cm. For fabric at least 10 cm wider than 1/4 chest measurement: 4 lengths + 1 sleeve length + 200 cm. These are rough estimates and should give you plenty of fabric for a basic shirt or blouse. Add more for gathering, design features like bias cuts, pleats, etc.
An isosceles triangle is a triangle with two congruent sides and congruent base angles. congruent means equal. No matter which direction the triangle's apex, or peak, points, it's an isosceles triangle if two of its sides are congruent.
In an isosceles triangle that has exactly two equal sides, the equal sides are called legs and the third side is called the base. The angle included by the legs is called the vertex angle and the angles that have the base as one of their sides are called the base angles. The vertex opposite the base is called the apex.