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Relations And Functions

Question
CBSEENMA12036056

If fk(x) = 1/k (sink x + cosk x), where x ε R and k ≥1, then f4 (x)-fo (x) equal to 

  • 1/6

  • 1/3

  • 1/4

  • 1/12

Solution

D.

1/12

Given comma space straight f subscript straight x left parenthesis straight x right parenthesis space equals space 1 over straight k space left parenthesis sin to the power of 4 space straight x space plus space cos to the power of straight k space straight x right parenthesis
where space straight x element of space straight R space and space straight k greater than 1
straight f subscript 4 left parenthesis straight x right parenthesis space minus straight f subscript 6 left parenthesis straight x right parenthesis space equals space 1 fourth space left parenthesis sin to the power of 4 space straight x space plus space cos to the power of 4 space straight x right parenthesis minus 1 over 6 space left parenthesis sin to the power of 6 straight x space plus space cos to the power of 6 space straight x right parenthesis
equals space 1 fourth left parenthesis 1 minus 2 sin squared straight x. cos squared straight x right parenthesis
minus 1 over 6 left parenthesis 1 minus 3 sin squared straight x. cos squared straight x right parenthesis space equals space 1 fourth minus 1 over 6 space equals space 1 over 12

Some More Questions From Relations and Functions Chapter

Show that the relation R in the set {1, 2, 3} given by R = {(1, 1), (2, 2), (3, 3), (1, 2), (2, 3)} is reflexive but neither symmetric nor transitive.

Show that the relation R in the set {1, 2, 3} given by R = {(1, 2), (2, 1)} is symmetric but neither reflexive nor transitive.

Give an example of a relation which is

(i) Symmetric but neither reflexive nor transitive.
(ii) Transitive but neither reflexive nor symmetric.
(iii) Reflexive and symmetric but not transitive.
(iv) Reflexive and transitive but not symmetric.
(v) Symmetric and transitive but not reflexive.

Let L be the set of all lines in a plane and R be the relation in L defined as R = {(L1, L2) : L1 is perpendicular to L2}. Show that R is symmetric but neither reflexive nor transitive.

 Determine whether each of the following relations are reflexive, symmetric and transitive :

(i) Relation R in the set A = {1, 2, 3,....., 13, 14} defined as

R = {(x, y) : 3 x – y = 0}

(ii) Relation R in the set N of natural numbers defined as R = {(x, y) : y = x + 5 and x < 4} (iii) Relation R in the set A = {1, 2, 3, 4, 5, 6} as R = {(x,y) : y is divisible by x} (iv) Relation R in the set Z of all integers defined as R = {(x,y) : x – y is an integer}

(v) Relation R in the set A of human beings in a town at a particular time given by
(a)    R = {(x, y) : x and y work at the same place}
(b)    R = {(x,y) : x and y live in the same locality}
(c)    R = {(x, y) : x is exactly 7 cm taller than y}
(d)    R = {(x, y) : x is wife of y}
(e)    R = {(x,y) : x is father of y}

Check whether the relation R defined in the set {1, 2, 3, 4, 5, 6} as R = {(a, b) : b = a + 1} is reflexive, symmetric or transitive.

Show that the relation R in R defined as R = {(a, b) : a ≤ b}, is reflexive and transitive but not symmetric.

Check whether the relation R in R defined by R = {(a,b) : a ≤ b3} is refleive, symmetric or transitive.

If R and R’ arc reflexive relations on a set then so are R ∪ R’ and R ∩ R’.