Let f, g : R → R be defined, respectively by f(x) = x + 1 and g(x) = 2x – 3. Find f + g, f – g and.
Find the domain in each case.
Given f(x) = x + 1 and g(x) = 2x – 3
Clearly, both f(x) and g(x) exist for all real values of x.
Hence, Domain of f = Domain of g = R
Range of f = Range of g = R
i. f + g
We know (f + g)(x) = f(x) + g(x)
⇒ (f + g)(x) = x + 1 + 2x – 3
∴ (f + g)(x) = 3x – 2
Domain of f + g = Domain of f ∩ Domain of g
⇒ Domain of f + g = R ∩ R
∴ Domain of f + g = R
Thus, f + g : R → R is given by (f + g)(x) = 3x – 2
ii. f – g
We know (f – g)(x) = f(x) – g(x)
⇒ (f – g)(x) = x + 1 – (2x – 3)
⇒ (f – g)(x) = x + 1 – 2x + 3
∴ (f – g)(x) = –x + 4
Domain of f – g = Domain of f ∩ Domain of g
⇒ Domain of f – g = R ∩ R
∴ Domain of f – g = R
Thus, f – g : R → R is given by (f – g)(x) = –x + 4
iii.
We know
Clearly, is defined for all real values of x, except for the case when 2x – 3 = 0 or
.
When,
will be undefined as the division result will be indeterminate.
Thus, domain of = R –
Thus, : R –
→ R is given by