How simplification work?

Hi,

I will share the code.

>> dw=(((the)/(2*st*sw))*(pr-pt)*(pr-pt))+(the*(1-((pr-pt)/st))*((pr-pt)/sw))

dw =

(the*(m - pr + w)^2)/(2*st*sw) - (the*((m - pr + w)/st + 1)*(m - pr + w))/sw

>> y=the*(((pr-pt)/sw)-((pr-pt)^2/(2*st*sw)))

y =

-the*((m - pr + w)/sw + (m - pr + w)^2/(2*st*sw))

>> x=dw-y

x =

the*((m - pr + w)/sw + (m - pr + w)^2/(2*st*sw)) - (the*((m - pr + w)/st + 1)*(m - pr + w)

Upon rearranging 'dw', we find that it is equal to 'y'. Hence, 'x' should be equal to zero. But that is not happening. Can anyone expain why!!