derivative of sqrt (1- X^2)

Question

I thought the answer was -x/(sqrt(1-x^2)) a site posted -2x / (sqrt(1-x^2))

Comments

the ans. will be :
-x / sqrt.[ (1-x^2)]
Its impossible to have this ans. -2x / (sqrt(1-x^2))
pls send the site address where u got this answer....

Answer 1

and you are right...they probably forgot to derivate x^2