# Math Help - derivatives of "arcs"

1. ## derivatives of "arcs"

how do you do this problem:
arctan(y^9)

2. You're expected to know that the derivative of $\arctan x$ equals $\frac1{1+x^2}.$ By the Chain Rule, we have that the derivative of $\arctan y^9$ equals $\frac1{1+y^{18}}\cdot(y^9)'.$