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Relations And Functions

Question
CBSEENMA12035651

Show that semi-vertical angle of a cone of maximum volume and given slant height is cos-1fraction numerator 1 over denominator square root of 3 end fraction.

Solution
Volume space of space cone space equals 1 third πr squared straight h
space equals 1 third straight pi left parenthesis space straight l space sin space straight alpha right parenthesis squared space left parenthesis space straight l space space cos space straight alpha right parenthesis
equals 1 third space straight pi space straight l cubed space sin squared space straight alpha space cos space straight alpha
dv over dα equals πl cubed over 3 left square bracket negative sin cubed space straight alpha space plus 2 sin space straight alpha space cosx space. cos space straight alpha right square bracket
equals fraction numerator straight pi space straight l cubed space sin space straight alpha over denominator 3 end fraction left parenthesis negative sin squared space straight alpha space plus space 2 space cos squared space straight alpha right parenthesis
For space maximum space volume

dv over dα space equals 0
fraction numerator πl cubed space sin space straight alpha over denominator 3 end fraction left parenthesis negative s i n space squared space alpha space plus 2 space c o s squared space alpha right parenthesis equals 0
s i n space alpha space not equal to 0
space 2 space c o s squared space alpha space equals space s i n squared space alpha
t a n squared space alpha space equals 2
t a n alpha space equals square root of 2
c o s space alpha space equals space fraction numerator 1 over denominator square root of 3 end fraction
alpha space equals space c o s to the power of negative 1 end exponent fraction numerator 1 over denominator square root of 3 end fraction
again space diff space straight w. straight r. straight t space straight alpha comma space we space get
fraction numerator straight d squared straight v over denominator dα squared end fraction space equals 1 third πl cubed cos squared space straight alpha left parenthesis 2 minus 7 space tan squared space straight alpha right parenthesis
at space cos space straight alpha space equals fraction numerator 1 over denominator square root of 3 end fraction
fraction numerator straight d squared straight v over denominator dα squared end fraction space less than 0
straight V space is space maximum space when space cos space straight alpha space equals fraction numerator 1 over denominator square root of 3 end fraction space or space straight alpha space equals cos to the power of negative 1 end exponent fraction numerator 1 over denominator square root of 3 end fraction

Some More Questions From Relations and Functions Chapter

If a matrix has 24 elements, what are the possible orders it can have ? Wh'at. if it has 13 elements ?

lf a matrix has 18 elements, what are the possible orders it can have ? What, if it has 5 elements?

If a matrix A has 12 elements, what arc the possible orders it can have 7 What if it has 7 elements ?

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}