Determining resistance of 3 resistors connected in delta configuration
The equations are easy to write down, but cumbersome to solve. 

When you have a triangle of 3 resistors (a, b, c), and nodes A, B, C. Resistor a is connected between nodes B &amp; C; resistor b between A &amp; C, and c between A &amp; B. Make 3 measurements -- AC, BC, and AB between nodes A&amp;C, B&amp;C and A&amp;B.

Mathematica gives this:

$$a-&gt;\frac{(-AB^2+2\cdot AB \cdot AC-AC^2+2\cdot AB\cdot BC+2\cdot AC\cdot BC-BC^2)}{2 \left(AB+AC-BC\right)}$$
$$b-&gt;\frac{(-AB^2+2\cdot AB\cdot AC-AC^2+2\cdot AB\cdot BC+2\cdot AC\cdot BC-BC^2)}{2 (AB-AC+BC)}$$
$$c-&gt;\frac{(AB^2-2\cdot AB\cdot AC+AC^2-2\cdot AB\cdot BC-2\cdot AC\cdot BC+BC^2)}{2 (AB-AC-BC)}$$