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.
An equilateral triangle is an isosceles triangle as it has 2 lengths that are equal and 2 equal sized angles. An isosceles triangle does not necessarily have to have equal lengths and angles do not have to be 60 degrees. So an equilateral triangle is an isosceles triangle but an isosceles triangle may not always be an equilateral triangle.