Assertion: The domain of the function f(x)=1|x|-x is (-∞,0).
Reason: If |x|>x, then x<0.
(1)
f(x)=1|x|-x
f is defined when |x|-x>0⇒|x|>x
Thus x must be negative.
∴ x∈(-∞,0)
∴ Both assertion and reason are true and reason is the correct explanation of assertion.