I did two problems just now and both had positive answers, while I mistakenly got negative answers.

The first, $\displaystyle 16x^2 - 16x^2 - 3x$

I thought it would equal 3x, since x - x = 0 and 0 - 3x = -3x

The other, $\displaystyle \frac{6x^2}{x^2-1}=6$ While I got the opposite answer.

Can anyone explainwhythese answers aren't positive?