[GreenKeys] slide rule rules??

[Craig Sawyers]

>  6.  (A - Q/2)^2  =  (D - Q/2)^2                           
> factor both sides
> of equation
> 
>  7.   A - Q/2       =    D - Q/2                              
>   take square
> root of both sides of

Gotcha!  Step 7 neatly ignores the other root, which is A + D = Q.

<grin>

Craig