Q.

If f(x)=2x and g(x)=x22+1, then which of the following can be discontinuous functions

1 f(x)+g(x)  
2 f(x)-g(x)  
3 f(x)·g(x)  
4 g(x)f(x)  

Ans.

(4)

Ans.    g(x)f(x)

Explanation:

We know that, if f and g are continuous functions, then

(1)   f+g is continuous.

(2)   f-g is continuous.

(3)   fg is continuous.

(4)   fg is continuous at those points where g(x)≠0

Here,  g(x)f(x)=x22+12x=x2+24x, which is discontinuous at x=0.