The length of the semiperimeter is commonly represented by s. Using the standard triangle labeling system, where side c is opposite angle C (thus, the length of AB), we can now represent the length of BX with (s - c). That is, the combined lengths of AB and BX make the semiperimeter, and we get an expression for BX by subtracting the length of AB. For identical reasons, we can devise similar expressions for the other segments shown below (Y and Z are, of course, the two other points of excircle tangency).