How to find the derivative of $\operatorname{arcsinh}(3x)$? I know 
The derivative of $\operatorname{arcsinh}(x) = 1/(x^2+1)^{1/2}$
But if I derivative $\operatorname{arcsinh}(3x)$ 
Why it doesn't equal to 
$(\operatorname{arcsinh}(3x))^{-1} (1/(9x^2+1)) (3)$ ??
Thanks all

Where did the factor $(\operatorname{arcsinh} (3x))^{-1}$ come from?  Alpha agrees with $\frac 3{\sqrt{9x^2+1}}$
