Mathematical Fallacy 2: Is $3458=1729$?

$\begin{aligned} 1729^2=&1729 \cdot 1729 \quad & \ldots (1) \\ 1729^2-1729^2=&1729 \cdot 1729-1729^2 \quad & \ldots (2) \\ (1729+1729)(1729-1729)=& 1729(1729-1729) \quad & \ldots (3) \\ (1729+1729)\cdot \cancel{0}=&1729\cdot \cancel{0} \quad & \ldots (4) \\ 3458=&1729 \end{aligned}$

The above shows my attempt to prove that $3458 = 1729$. In which of these steps did I make a flaw in my logic?