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If the length of the hypotenuse is called A, and the lengths of the other two sides are called B and C, then A2 = B2 + C2. By using accurate measurement of distances and angles, and applying Pythagorasis theorem, it is possible to easily determine distances that are otherwise difficult to measure accurately. The process of measuring things in this way is called triangulation. It is very easy to convince yourself that the theory is true: just draw some right triangles and do the calculations. For example, using graph paper and a ruler, one can easily draw a triangle whose right-angled sides are three units and four units long (the units donit matter and can be centimeters, inches, feet, yards, meters, anything). The hypotenuse that joins the ends of these two lines will be five units in length.
Using this method it is possible to accurately draw lines whose lengths are difficult to measure. This is a commonly-used trick for indeterminate numbers such as the square roots of 2, 3, 5, 7, and others.