You cannot identify congruent triangles with only angles Angle-Angle-Angle is not one of the rules of congruence. They could have different sizes with the same angles which doesn't makes them congruent. They are similar though. Once you find the missing angles with the equations 62+39+C=180 and 39+79+X=180 the corresponding angles are congruent. So the triangles are not congruent, but are similar.
function composition is an operation that takes two functions f and g and produces a function h such that h(x) = g(f(x)). In this operation, the function g is applied to the result of applying the function f to x.
