What is the answer to 2y-8x=20

Pick a number.  Any number.  Call it 'x'.

Multiply 'x' by  4.
Add  10  to the product.
Call the current number  'y'.

The 'x' and 'y' that you have now are an 'answer' to that equation.

Do it as many times as you like.  There are an infinite number of them.

The nth term = n^2 - 2n - 3.

Step-by-step explanation:

                     -4 -3  0  5  12  21  32

Differences      1  3  5  7    9    11

Difference         2 2   2   2    2    <-- divide this by 2 so its n^2.

So the first term is n^2

List the original numbers  and values of n^2:

sequence   -4  -3  0   5    12    21   32

n^2               1    4  9   16  25   36   49

Subtract      -5  -7 -9  -11   -13   -15    -17

These last numbers have a common difference of -2 so the next part of the answer is -2n and get the  -5, -7 etc we add -3.

So our formula is n^2 - 2n - 3.

Check for the 3rd term:

3rd term is  3^2 - 2(3) - 3 = 0.

5th term = 5^2 - 2(5) - 3 =  25 - 10 - 3 = 12.