Q.

Assertion: The domain of the function f(x)=1|x|-x is (-∞,0).

Reason: If |x|>x, then x<0.

1 Both assertion and reason are true and reason is the correct explanation of assertion.  
2 Both assertion and reason are true but reason is not the correct explanation of assertion.  
3 Assertion is true but reason is false.  
4 Assertion is false but reason is true.  

Ans.

(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.