Right angles are usually always 90 degrees, then if you are looking at right triangles, you have 45,45,90 degree triangles and 30,60,90 triangles
A formula is recursive if it expresses the term
in terms of the previous one(s) 
In this case, every term is 7 more than the previous one, so the formula for
will only involve
:

In fact, this formula is simply saying: for every index
, the term with that index is 7 more than the term before.
Also, we have to specify the starting point (otherwise we would go backwards indefinitely), so the complete recursive formula is

which means: start with 2 and generate every other term by adding 7 to the previous one.
Answer:
b = -27
Step-by-step explanation:
-1/3 b = 9
Multiply each side by -3
-3 * -1/3 b = -3 * 9
b = -27
Answer : A
hope this helps