Question

I a making an ex: and see this: tan x = -1 <=> - tan x (pi/4) Why is the - before tan?

Answer 1

for x?

Answer 2

- tan x (pi/4) why is is not tan (-pi/4)

Answer 3

It could just as well be tan (-pi/4), because tan is an uneven function: f(-x) = -f(x) for all x in the domain of f.
I guess the reason -tan(pi/4) is used because you are supposed to know by heart that tan(pi/4) = 1.
So we have:
tan(x) = -1 <=>
-tan(x) = 1 <=>
tan(-x) = 1 <=>
tan(-x) = tan(pi/4 + k*pi) <=>
-x = pi/4 + k*pi <=>
x = -pi/4 - k*pi which is the same as x = -pi/4 + k*pi, because k is any integer.

Hope this helps...

ZeHanz