Given one side of a triangle, as well as the radius of the circumscribed circle and the radius of the inscribed circle. What are the lengths of the other two sides? (Numerical example: units.) (Try to solve without using trigonometric tables!)
Solution
We denote the center of the circumscribed circle of the written, circumscribed circle by , the midpoint of by , the projection of onto by , the intersection of with and the circumscribed circle by and , the point opposite to by . It is known that
since, for example, the angle and the angle are each equal to half the sum of the angles at and of the triangle . We can assume that under the condition; if we omit this condition, the roles of and can naturally be swapped. The in (4) is the root of the equation (1). From this, we get based on (2), assuming that a positive number stands on the right side of (2). Therefore, the number of possible solutions can be any number between 0 and 4.
In the numerical case mentioned, (1) represents the equation
from which . Accordingly, based on (2),
and a negative value is obtained for . Finally, from (4), we get
Remark. In the publication, the value of was given as 79 due to a typographical error (the correct text appeared in the Russian and English translations). From this, we get the values , and ( is also negative here).