How many possible equivalence classes of triangles might exist given some specific given measures of SAS (side angle side) triangle measures in these geometries? a. Euclidean b. Hyperbolic c. Taxicab d. Spherical

In Euclidean geometry, two triangle two pairs of sides of equal length and one pair of equal angle are said to be congruent by SAS law. 

Let T be the set of all triangles in Euclidean plane. The relation $\cong$ congruence on T is an equivalence relation

Therefore, one equivalence class of triangles exists given some specific measures of SAS which is 

$S=\left\{T_i\in T:T_i\cong T_j\right\}$

In hyperbolic plane, SAS congruence is a natural postulate also. Therefore, in this plane also, two triangles with two pairs of sides of equal length and one pair of equal angle are congruent. 

Therefore, there is one equivalence class of triangles in hyperbolic geometry given some specific measures of SAS which is  $S=\left\{T_i\in T_H:T_i\cong T_j\right\}$ where $T_H$ is the set of all triangles in this plane.