Question

Let f(x)=ln(cos x). Assume that x is restricted so that ln is defined. Find f ' (π/2).

Answer 1

f(x)=ln(cos x)
f ' (x) = 1/cosx .(-sinx)
= -sinx/cosx
now just substitute x with π/2

Answer 2

I got that far...the problem is that when I plug in pi/2. it says error

Answer 3

my hw (which is electronic) allows for multiple attempts...i have tried -1/0 or DNE. I was thinking maybe i did something wrong

Answer 4

just tried undefined...that worked...thats for your help rizwan_uet :)

Answer 5

thank*