If ∆PQR is congruent to ∆STU (Fig. 6.20), then what is the length of TU?

By which congruency criterion, the two triangles in Fig. 6.19 are congruent?

By which of the following criterion two triangles cannot be proved congruent?

If ∆ABC and ∆DBC are on the same base BC, AB = DC and AC = DB (Fig. 6.21), then which of the following gives a congruence relationship?

Fill in the blanks to make the statements true.

The ________ triangle always has altitude outside itself.