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Relations And Functions

Question
CBSEENMA12035775

If xm yn = (x + y)m + n, prove that fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space 0

Solution

We are given,
If xm yn = (x + y)m + n
Taking log on both sides, we get
log xm yn = log(x + y)m + n
log xm + log yn = m+n log(x + y)
m logx + n logy = m+n log (x+y)

Differentiating above equation w.r.t. x, we get

 straight m over straight x space plus straight n over straight y dy over dx space equals space fraction numerator left parenthesis straight m plus straight n right parenthesis over denominator left parenthesis straight x plus straight y right parenthesis end fraction space space straight x space open parentheses 1 plus dy over dx space close parentheses
straight n over straight y dy over dx minus open parentheses fraction numerator straight m plus straight n over denominator straight x plus straight y end fraction close parentheses dy over dx space equals space open parentheses fraction numerator straight m plus straight n over denominator straight x plus straight y end fraction close parentheses minus straight m over straight x
open parentheses straight n over straight y minus fraction numerator straight m plus straight n over denominator straight x plus straight y end fraction close parentheses dy over dx space equals space fraction numerator straight x left parenthesis straight m plus straight n right parenthesis minus straight m left parenthesis straight x plus straight y right parenthesis over denominator straight x left parenthesis straight x plus straight y right parenthesis end fraction
open parentheses fraction numerator nx plus ny minus my minus ny over denominator straight y left parenthesis straight x plus straight y right parenthesis end fraction close parentheses dy over dx space equals space fraction numerator xm plus xn minus mx space minus my over denominator straight x space left parenthesis straight x plus straight y right parenthesis end fraction
dy over dx space equals space straight y over straight x space straight x fraction numerator left parenthesis xn minus my right parenthesis over denominator left parenthesis xn minus my right parenthesis end fraction
rightwards double arrow space dy over dx space equals space straight y over straight x
And fraction numerator begin display style space straight d squared straight y end style over denominator dx squared end fraction space equals space fraction numerator straight x begin display style dy over dx end style minus straight y over denominator straight x squared end fraction
space equals space fraction numerator straight x begin display style straight y over straight x end style minus straight y over denominator straight x squared end fraction
space equals space 0

Some More Questions From Relations and Functions Chapter

Let A be the set of all students of a boys school. Show that the relation R in A given by R = {(a, b) : a is sister of b} is the empty relation and R’ = {(a, b) : the difference between heights of a and b is less than 3 meters} is the universal relation.

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.