Double integral denominator error in solution

[Chandasouk]

http://img844.imageshack.us/img844/3293/17693169.jpg

I follow it up to the third step, but how did they get the bottom denominators of -4? shouldn't it be -1?

 

[rock.freak667]

∫(ax+b)ⁿdx = (1/a(n+1))(ax+b)ⁿ⁺¹+C

In their case, n=-2 and a=4

 

[Chandasouk]

Oh, should I know that formula or do most people look that up in a table? Been a while since I did Calc 2.

 

[Mark44]

Oh, should I know that formula or do most people look that up in a table? Been a while since I did Calc 2.

You don't need to know that formula, but you should know how to derive it. rockfreak.667 used a very simple substitution to get it.