Question 1:
In ΔSTU and ΔDEU,
[tex] \frac{SU}{DU} = \frac{39}{16} [/tex] ≠ [tex] \frac{40}{16} = \frac{TU}{EU} [/tex]
∠SUT = ∠DUE [ Opposite angles ]
Thus, ΔSTU and ΔDEU are NOT similar. as the ratio of the length of the sides is not a constant.
Question 2:
In ΔABC and ΔHGF,
[tex] \frac{AB}{HG} = \frac{72}{12} = 6 [/tex]
[tex] \frac{AC}{HF} = \frac{84}{14} = 6[/tex]
[tex] \frac{BC}{GF} = \frac{48}{8} = 6[/tex]
Thus, [tex] \frac{AB}{HG}= \frac{AC}{HF} = \frac{BC}{GF} = 6[/tex]
Hence, ΔABC and ΔHGF are similar by SSS similarity criterion.