<PRE><B>Question 1184674</B>
&lt;pre&gt;
Set them identically &quot;≡&quot; (not conditionally &quot;=&quot;) equal.

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ a-(x+b)&lt;sup&gt;2&lt;/sup&gt;

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ a-(x&lt;sup&gt;2&lt;/sup&gt;+2bx+b&lt;sup&gt;2&lt;/sup&gt;)

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ a-x&lt;sup&gt;2&lt;/sup&gt;-2bx-b&lt;sup&gt;2&lt;/sup&gt;)

Add x&lt;sup&gt;2&lt;/sup&gt; to both sides:

6x ≡ a-2bx-b&lt;sup&gt;2&lt;/sup&gt;

Now here is where we can do something in identity equations 
that we cannot do in a conditional equations.  That is, in 
identity equations we can equate coefficients of like powers 
of x (as well as constant terms).

The coefficient of x on the left is 6 and the coefficient
of x on the right is -2b, and since this is an identity
equation and not a conditional equation, we can set 6 and
-2b (conditionally) equal to each other:

 6 = -2b
-3 = b

Now we substitute -3 for b

6x ≡ a-2bx-b&lt;sup&gt;2&lt;/sup&gt;
6x ≡ a-2(-3)x-(-3)&lt;sup&gt;2&lt;/sup&gt;
6x ≡ a+6x-9
 9 ≡ a

Now let&#39;s check to see if we have an identity equation by 
substituting:

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ a-(x+b)&lt;sup&gt;2&lt;/sup&gt;

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ 9-[x+(-3)]&lt;sup&gt;2&lt;/sup&gt;

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ 9-(x-3)&lt;sup&gt;2&lt;/sup&gt;

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ 9-(x&lt;sup&gt;2&lt;/sup&gt;-6x+9)

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ 9-x&lt;sup&gt;2&lt;/sup&gt;+6x-9

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ -x&lt;sup&gt;2&lt;/sup&gt;+6x

6x-x&lt;sup&gt;2&lt;/sup&gt; ≡ 6x-x&lt;sup&gt;2&lt;/sup&gt;

Yep, both sides are identical!

Edwin&lt;/pre&gt;</PRE>