False Proof

People said that looking for people mistake is easier than our own mistake. So here is a false proof, and spot the mistake.

$-12=-12$

$9-21=16-28$

$9-21+\frac{49}{4}=16-28+\frac{49}{4}$

$(3)^2-2\cdot 3 \cdot \frac{7}{2}+(\frac{7}{2})^2=(4)^2-2\cdot 4 \cdot \frac{7}{2}+(\frac{7}{2})^2$

$(3-\frac{7}{2})^2=(4-\frac{7}{2})^2$

$3-\frac{7}{2}=4-\frac{7}{2}$

$3=4$

Check the discussion in my video https://youtu.be/N_LIFwF35xA