Cabn someone help with this

Acircle has a circumference of 28.36 units what is the diameter of the circle

Bella want to know what the students at her school think of her show. which is the best group to survey to find this information a. go to the mall and ask all of the students she recognizes from school b. ask her viewers to call in durning an episode of the show c. get a list of students at her school from the office and use a random number generator to pick 30 of them d. get a list of students at her school from the office and pick the first 30 students on the list

State one method by which you can recognize a perfect square trinomial.