Let f : [0, ∞) → R and g : R → R be defined by and g(x) = x. Find f + g, f – g, fg and
Given and g(x) = x
Domain of f = [0, ∞)
Domain of g = R
i. f + g
We know (f + g)(x) = f(x) + g(x)
Domain of f + g = Domain of f ∩ Domain of g
⇒ Domain of f + g = [0, ∞) ∩ R
∴ Domain of f + g = [0, ∞)
Thus, f + g : [0, ∞) → R is given by
ii. f – g
We know (f – g)(x) = f(x) – g(x)
Domain of f – g = Domain of f ∩ Domain of g
⇒ Domain of f – g = [0, ∞) ∩ R
∴ Domain of f – g = [0, ∞)
Thus, f – g : [0, ∞) → R is given by
iii. fg
We know (fg)(x) = f(x)g(x)
Clearly, (fg)(x) is also defined only for non-negative real numbers x as square of a real number is never negative.
Thus, fg : [0, ∞) → R is given by
iv.
We know
Clearly, is defined for all positive real values of x, except for the case when x = 0.
When x = 0, will be undefined as the division result will be indeterminate.
⇒ Domain of = [0, ∞) – {0}
∴ Domain of = (0, ∞)
Thus, : (0, ∞) → R is given by