How many different 99-letter permutations can be formed from 77 identical h's and two identical t's?

What is the area of the trapezoid shown ?

She was given that ∠a ≅ ∠edf, and has already proven segment (ab) ≅ segment (de). which pair of corresponding parts and triangle congruency method would not prove δabc ≅ δdef?

Aquadratic equation has exactly one real number solution . witch is the value of its discriminant ? -1012