What Is Wrong with This Differentiation?

[yungman]

I am confuse with this:

$$Let\;\; t=jx \;\;,\;\; j =\sqrt{-1}$$

$$\Rightarrow \frac{dt}{dx}=j$$

But if I use $$t^2=-x^2 \;\Rightarrow\; 2t\frac{dt}{dx}=-2x$$

$$\Rightarrow \frac{dt}{dx}=-\frac{x}{t}$$

What is wrong?

 

[rock.freak667]

sub back t=jx, and then multiply by j/j

 

[yungman]

sub back t=jx, and then multiply by j/j

Nice!

Thanks