Answer : 
Given expression is 
To make perfect square trinominal we use completing the square method
In completing the square method we add and subtract the half of square of coefficient of middle term
Here coefficient of middle term is -7
Half of -7 is 
Square of
is
=
So the expression becomes
that gives perfect square trinomial
Hence , the value of 'c' is
I believe it’s a trapezoid but i’m not too sure... sorry :((
Answer:
The explicit rule is:
Step-by-step explanation:
The explicit rule is given by:

The given sequence is 25,21,17,13

d=21-25
d=-4
We plug in the values into the formula to get;



i hope i have been useful buddy.
good luck ♥️♥️♥️♥️♥️.