Is function f times g continuous at x=1 if f is not continuous at x=1?  f=3x+5 when x < equal to 1 f=x^1/2 +3 when x > 1 g= x^2-3x+2 when x < equal to 1 g =lnx when x>1

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embizze | High School Teacher | (Level 2) Educator Emeritus

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A function is continuous at a point x=c if

(1) `lim_(x->c)` exists

(2) f(c) exists

(3) `f(c)="L"=lim_(x->c)`

We are trying to determine if fg(x) is continuous at x=1:

(1) `lim_(x->1)fg(x)=0` From the left we find `lim_(x->1^-)fg(x)=(3x+5)(x^2-3x+2)==>fg(1)=0`

From the right we determine `lim_(x->1^+)fg(x)=lim_(x->1^+)(sqrt(x)+3)(lnx)=0`

So the limit exists and is 0.

(2) The value of the function fg(1)=0 exists.

(3) The value of the function at x=1 is the same as the limit as x approaches 1.

Therefore, the function fg(x) is continuous at x=1.

The graph of f(x) in red, g(x) in blue, and fg(x) in purple: