Step-by-step explanation:
Recall that
[tex]\sin(-x) = -\sin x[/tex]
Therefore,
[tex]\csc(-x) = \dfrac{1}{\sin(-x)} = -\dfrac{1}{\sin x}[/tex]
so
[tex]\csc(-x)\tan x = \left(-\dfrac{1}{\sin x}\right)\left(\dfrac{\sin x}{\cos x}\right)[/tex]
[tex]\:\:\:\:\:\:\:\:\:= -\dfrac{1}{\cos x} = -\sec x[/tex]
