A letter, which is how you name it. If that is what your asking, of course.
Answer:
10
Step-by-step explanation:
The answer is the first one; it is an arithmetic sequence with a common difference of -40.
Answer:
Use pythagoreum theorem to determine whether it is or isn't since I'm not really sure myself but here's my calculations.
Step-by-step explanation:
We need to find AC.
Picture a triangle called ABC. AB is one side and BC the other while AC is the hypotenuse.
AC=

Round up the 7.6 to a whole number and you get AC=8. To get perimeter of a triangle simply add the sides together to get 18.
Not really sure about my answer but hope this helped.