FROM THE GIVEN RELATIONS FIND FOG AND GOF WORKSHEET

Problem 1 :

Functions f and g are defined as follows :

f = {(0, 2), (1, 3), (2, 0), (3, 1)}

g = {(0, 3), (1, 2), (2, 1), (3, 0)}

Find a) f g

b) g f

c) f f

Solution

Problem 2 :

f and g are defined as :

f = {(0, 3), (1, 0), (2, 1), (3, 2)}

g = {(0, 1), (1, 2), (2, 3), (3, 0)}

Find f g

Solution

Problem 3 :

f and g are defined as :

f = {(0, 2), (1, 5), (2, 7), (3, 9)}

g = {(2, 2), (5, 0), (7, 1), (9, 3)}

Find a) f g    b) g f

Solution

Problem 4 :

a) If ax + b = cx + d for all values of x, show that a = c and b = d.

Hint : if it is true for all x, it is true for x = 0 and x = 1.

b) Given, f(x) = 2x + 3 and g(x) = ax + b and that (f g) (x) = x for all values of x, deduce that a = 1/2 and b = -3/2.

c) Is the result in b true if (g f) (x) = x for all x ?

Solution

Answer Key

1)  a) Finding fog :

fogandgofq1p3

(f g) (0) = 1

(f g) (1) = 0

(f g) (2) = 3

(f g) (3) = 2

f g = {(0, 1), (1, 0), (2, 3), (3, 2)}

b) Finding gof :

findgofq1p1

(g f) (0) = 1

(g f) (1) = 0

(g f) (2) = 3

(g f) (3) = 2

g f = {(0, 1) (1, 0) (2, 3) (3, 2)}

c) Finding fof :

findfogq1p1

(f f) (0) = 0

(f f) (1) = 1

(f f) (2) = 2

(f f) (3) = 3

f f = {(0, 0), (1, 1), (2, 2), (3, 3)}

2)

findfogq2p3.png

(f g) (0) = 0

(f g) (1) = 1

(f g) (2) = 2

(f g) (3) = 3

f g = {(0, 0), (1, 1), (2, 2), (3, 3)}

3)

a)  f  g :

findfogq3p3

(f g) (0) = 2

(f g) (1) = 0

(f g) (2) = 1

(f g) (3) = 3

f g = {(0, 2), (1, 0), (2, 1), (3, 3)}

b)  g  f :

findfogq3p4.png

(g f) (2) = 7

(g f) (5) = 2

(g f) (7) = 5

(g f) (9) = 9

g f = {(2, 7), (5, 2), (7, 5), (9, 9)}

4) a)  a = c

b) a = 1/2 and b = -3/2

c)  So, the result in b is true.

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