The area of a rectangle is the result of multiplying its length times its width. So the rectangles length and width are factor pairs of the area.
The number 36 has four non-equal, whole number factor pairs: (1,36) ; (2,18) ; (3,13) ; (4,9)
*note : (6,6) makes a square not rectangle
The number 15 has only two whole number factor pairs (1,15) and (3,5)
<em>2x - 5 + 3x = 35
</em>
<em>simplify
</em>
<em>5x - 5 = 35
</em>
<em>add 5 to both sides
</em>
<em>5x - 5 + 5 = 35 + 5
</em>
<em>simplify
</em>
<em>5x = 40
</em>
<em>divide both sides by 5
</em>
<em>5x/5 = 40/5
</em>
<em>simplify
</em>
<em>x = 8
</em>
<em>
</em>
<em />
Based on these first few terms, we can deduce that the next term is computed by switching the sign of the previous one, and multiplying it by 3: we start with -1, we switch the sign (1) and multiply by 3 (3); then again we switch the sign (-3) and multiply by 3 (-9), and so on.
Since switching sign is the same as multiplying by -1, we can compute every next term by multiplying the previous one by -3:

So, the recursive formula is

because it states precisely that the next term is -3 times the previous one.