1) y=sqrt(1-x^2)
y' =1/(sqrt(1-x^2))*(-x)=-x/sqrt(1-x^2)
2) y=ln(1+cos(x))
y'=(1/(1+cos(x))*(-sin(x)=-sin(x)/(1+cos(x))
1) y=sqrt(1-x^2)
y' =1/(sqrt(1-x^2))*(-x)=-x/sqrt(1-x^2)
2) y=ln(1+cos(x))
y'=(1/(1+cos(x))*(-sin(x)=-sin(x)/(1+cos(x))