we have the equation
tan(x) (tan x + 1) = 0
this equation is satisfied when
tan(x)=0
and
(tanx+1)=0
Remember that
the tanx is zero when the sine is zero
so
x=0,pi, 2pi,3pi,...
x=(+/-)npi
and
(tanx+1)=0
when
the value of tanx=-1
so
x=-pi/4 --------> pi/4(+/-)npi
therefore
