We know that if two triangles are congruent then by we apply the CPCTC property which says that the corresponding parts of congruent triangles are congruent.
Since, ∆AMH ≅ ∆HTA
⇒ The corresponding angles of ∆AMH and ∆HTA congruent.
⇒∠AMH is congruent to ∠HTA [ Keep order of letters same]
In a fraction, it doesnt matter where the negative is. Since we have a single negative sign, our answer must also have a single negative. (2 negative signs will cancel each other out.)