further rates question (1 Viewer)

[waltssillyhat]

For the first part of this question, can someone explain how the solution got dtheta/dx? I know they used chain rule with inverse tan, but that would give me
-sec^2(x/l) / tan^2(x/l), so I don't understand what they substituted to get that answer.

 

[coolcat6778]

View attachment 48925View attachment 48926
For the first part of this question, can someone explain how the solution got dtheta/dx? I know they used chain rule with inverse tan, but that would give me
-sec^2(x/l) / tan^2(x/l), so I don't understand what they substituted to get that answer.

d/dx arctan(x/a) = a/a^2+x^2