What is the practical domain for the function f(x)?

Which triangle congruence postulate or theorem justifies my claim that the steps i made using construction paper and scissors produce an isosceles triangle? was it sss, sas, asa, aas, or hl?

Write the factored form of this trinomial 9x^2+18x-7

Asa a yogurt shop allows its customers to add, for no charge, 3 toppings to any yogurt purchased. if the store has 18 possible toppings, how many different 3-topping combinations can a customers choose?