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 isosceles because it has three equal sides and an isosceles must have two, which an equilateral does. However, an isosceles has 2 equal sides and therefore is not an equilateral because an equilateral must have 3 equal sides. Simply: an equilateral triangle is an isosceles triangle because 3 is greater than or equal to 2 and an isosceles triangle is not an equilateral triangle because 2 is not greater than or equal to 3. Hope this helps.