Questions on Functions with Solutions
Several questions on functions are presented and their detailed solutions discussed. The questions cover a wide range of concepts related to functions such as definition, domain, range, evaluation, composition and transformations of the graphs of functions.
Question 1: Is the graph shown below that of a function?
graph of question 1
Solution to Question 1:
Vertical line test: A vertcal line at x = 0 for example cuts the graph at two points. The graph is not that of a function.
Question 2: Does the equation
y 2 + x = 1
represents a function y in terms of x?
Solution to Question 2:
Solve the above equation for y
y 2= 1 - x
y = + SQRT(1 - x) or y = - SQRT(1 - x)
For one value of x we have two values of y and this is not a function.
Question 3: Function f is defined by
f(x) = - 2 x 2 + 6 x - 3
find f(- 2).
Solution to Question 3:
Substitute x by -2 in the formula of the function and calculate f(-2) as follows
f(-2) = - 2 (-2) 2 + 6 (-2) - 3
f(-2) = -23
Question 4: Function h is defined by
h(x) = 3 x 2 - 7 x - 5
find h(x - 2).
Solution to Question 4:
Substitute x by x - 2 in the formula of function h
h(x - 2) = 3 (x - 2) 2 - 7 (x - 2) - 5
Expand and group like terms
h(x - 2) = 3 ( x 2 - 4 x + 4 ) - 7 x + 14 - 5
= 3 x 2 - 19 x + 7
Question 5: Functions f and g are defined by
f(x) = - 7 x - 5 and g(x) = 10 x - 12
find (f + g)(x)
Solution to Question 5:
(f + g)(x) is defined as follows
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(f + g)(x) = f(x) + g(x) = (- 7 x - 5) + (10 x - 12)
Group like terms to obtain
(f + g)(x) = 3 x - 17
Question 6: Functions f and g are defined by
f(x) = 1/x + 3x and g(x) = -1/x + 6x - 4
find (f + g)(x) and its domain.
Solution to Question 6:
(f + g)(x) is defined as follows
(f + g)(x) = f(x) + g(x)
= (1/x + 3x) + (-1/x + 6x - 4)
Group like terms to obtain
(f + g)(x) = 9 x - 4
The domain of function f + g is given by the intersection of the domains of f and g
Domain of f + g is given by the interval (-infinity , 0) U (0 , + infinity)
Question 7: Functions f and g are defined by
f(x) = x 2 -2 x + 1 and g(x) = (x - 1)(x + 3)
find (f / g)(x) and its domain.
Solution to Question 7:
(f / g)(x) is defined as follows
(f / g)(x) = f(x) / g(x) = (x 2 -2 x + 1) / [ (x - 1)(x + 3) ]
Factor the numerator of f / g and simplify
(f / g)(x) = f(x) / g(x) = (x - 1) 2 / [ (x - 1)(x + 3) ]
= (x - 1) / (x + 3) , x not equal to 1
The domain of f / g is the intersections of the domain of f and g excluding all values of x that make the numerator equal to zero. The domain of f / g is given by
(-infinity , -3) U (-3 , 1) U (1 , + infinity)
Question 8: Find the domain of the real valued function h defined by
h(x) = SQRT ( x - 2)
Solution to Question 8:
For function h to be real valued, the expression under the square root must be positive or equal to 0. Hence the condition
x - 2 >= 0
Solve the above inequality to obtain the domain in inequality form
x >= 2
and interval form
[2 , + infinity)
Question 9: Find the domain of
g(x) = SQRT ( - x 2 + 9) + 1 / (x - 1)
Solution to Question 9:
For a value of the variable x to be in the domain of function g given above, two conditions must be satisfied: The expression under the square root must not be negative
- x 2 + 9 >= 0
and the denomirator of 1 / (x - 1) must not be zero
x not equal to 1
or in interval form
(-infinity , 1) U (1 , + infinity)
The solution to the inequality - x 2 + 9 >= 0 is given by the interval
[-3 , 3]
Since x must satisfy both conditions, the domain of g is the intersection of the sets