Considering the following table ...

a | b | c | d
---------------------
256 | 80 | 4 | 0
704 | 80 | 11 | 7
288 | 512 | 0 | 5
736 | 512 | 7 | 12

Given a pair of values for a and b, I derived the following to solve for
c and d ...

c = ( ( a - 256 ) / 64 ) - ( ( b - 464 ) / 96 )
d = ( ( a - 256 ) / 64 ) + ( ( b - 80 ) / 96 )

But given a pair of values for c and d, I am having difficulty finding a
and b. I came up with the following but it is incorrect. any help would
be appreciated, thank you.

a = ( ( c * 64 ) + 256 ) + ( ( d * 96 ) + 464 )
b = ( ( c * 64 ) + 256 ) - ( ( d * 96 ) + 80 )

"Bill" <Bill@hotmail.com> wrote in message
news:UGuVg.18477$vi3.11646@bignews3.bellsouth.net. ..

Try:

a = 32*(c + d) + 128

b = 48*(d - c) + 272

Greg Neill wrote:

Works perfectly! You are brilliant, thank you Greg!

> Try:

Greg,

Could you please explain to me step by step how you arrived at that
answer? Thank you

"Bill" <Bill@hotmail.com> wrote in message
news:8BrXg.41972$tT6.32387@bignews7.bellsouth.net. ..

Sure. I started with your equations:

c = ( ( a - 256 ) / 64 ) - ( ( b - 464 ) / 96 ) (1)
d = ( ( a - 256 ) / 64 ) + ( ( b - 80 ) / 96 ) (2)

(first verifying that they did in fact produce
the correct values for c and d...)

Then I assumed that c and d were now constant
values and solved the pair for a and b:

Start with (1) and rearrange for a:

(a - 256)/64 = c + (b - 464)/96

a - 256 = 64*c + (b - 464)*64/96

a = 64*c + (2/3)*b - 160/3 (3)

Now substitute this expression for a into (2):

d = ([64*c + (2/3)*b - 160/3] - 256)/64 + (b - 80)/96

d = c - 29/6 + b/96 + (b-80)/96

d = c + b/48 - 17/3

Rearrange for b:

b = 48*d - 48*c + 272

b = 48*(d - c) + 272 (4)

Now use this value for b in equation (3):

a = 64*c + (2/3)*[48*(d - c) + 272] - 160/3

a = 32*(c + d) + 128 (5)

And there you have it.