The common difference, d, can be determined by subtracting the two consecutive values:
1 - 5 = -4
-3 - 1 = -4
-7 - -3 = -4
Then, using the equation:
an = a1+ d(n-1)
a_21 = 5 + (-4)(21 - 1)
a_21 = -75
The answer is letter D. I hope I was able to help you. Have a good day!
See the attached picture.
First calculate the length of each side.
Using the side length multiply by the number of sides to find the perimeter.
Then the area is 1/2 x perimeter x apothem.
I’m positive the answer is B if it isn’t I’m sorry
3x-5(8)=2
3x-40=2
3x=40+2
3x=42
x=14