Identity Check
1. Let's state the problem: Verify the given algebraic identity:
$$((sx+y)(z^2+w^2))^2 = (s+y)^2 + 2(s+y)(z^2+w^2) + (z^2+w^2)^2$$
2. First, let's expand the left side:
$$((sx + y)(z^2 + w^2))^2 = ((sx + y)(z^2 + w^2))\cdot((sx + y)(z^2 + w^2))$$
3. Multiply inside the parentheses:
$$(sx + y)(z^2 + w^2) = sx \cdot z^2 + sx \cdot w^2 + y \cdot z^2 + y \cdot w^2 = sx z^2 + sx w^2 + y z^2 + y w^2$$
4. So, the expression becomes:
$$(sx z^2 + sx w^2 + y z^2 + y w^2)^2$$
5. This is a square of a sum of four terms; expanding will be lengthy and includes cross terms.
6. Now examine the right side:
$$(s + y)^2 + 2(s + y)(z^2 + w^2) + (z^2 + w^2)^2$$
7. Notice that the right side resembles the expansion of $(a + b)^2 = a^2 + 2ab + b^2$ where $a = s + y$ and $b = z^2 + w^2$.
8. But the left side has $(sx + y)$ instead of $(s + y)$, so the expressions are not the same unless $x=1$.
9. Therefore the original equality holds only if $x=1$ and $s$ replaces $sx$ accordingly.
10. Hence the correct identity for general $x$ is:
$$((s x + y)(z^2 + w^2))^2 \neq (s + y)^2 + 2(s + y)(z^2 + w^2) + (z^2 + w^2)^2$$
unless $x=1$ and the expression is:
$$( (s + y)(z^2 + w^2))^2 = (s + y)^2 (z^2 + w^2)^2 = (s + y)^2 (z^2 + w^2)^2$$
which is not equal to the right side either, because the right side is a sum of squares and cross terms rather than a product squared.
11. Therefore, the given equality is false in general.
Final answer: The equation
$$((s x + y)(z^2 + w^2))^2 = (s + y)^2 + 2(s + y)(z^2 + w^2) + (z^2 + w^2)^2$$
is false for general variables.