Answer:
-5
Step-by-step explanation:
To find the common difference, take the second term and subtract the first term
-2 - 3 = -5
Check with the third term and the second term
-7 - (-2) = -7 +2 = -5
The common difference is -5
Answer:
B. -2t^2+3t+4
Step-by-step explanation:
The standard form as
ax^2 + bx + c
Option B meets that requirement, even though it has a '-' in front

We know that
and 
Substitute in the value. 
Use a calculator to multiply. 
The polygon is built of 7 triangles (picture).