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Answer 1 · 2018-01-09T17:25:28

Check below.

#f(x)=x+log(cosx)#

Set #g(x)=logx# , #D_g=(0+oo)#

For #f# to be defined in #RR# we need:

#(cosx)##in##D_g#

so #cosx>0#

#cosx=0# #<=># #x=kπ+-π/2# , #k##in##ZZ#

So one could say that #D_f={AA##x##in##RR#: #-π/2##<##x-2kπ##<π/2}# , #k##in##ZZ#

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