Numerical example

If \(a=2\) and \(b=5\), then \((a+b)=(2+5)=7\).
It follows that \((a+b)^2=(a+b) \cdot (a+b)=(7) \cdot (7)=(7)^2=49\).
On the other hand, \(a^2+b^2=(2)^2+(5)^2=4+25=29\).
This numerical example shows that \((a+b)^2 \neq a^2+b^2\).