Sponsor Area

Continuity And Differentiability

Question
CBSEENMA12035496

Verify the truth of Rolle's Theorem for the function
straight f left parenthesis straight x right parenthesis equals space sin space 3 straight x comma space straight x element of open square brackets 0 comma space straight pi over 3 close square brackets

Solution
Here space straight f left parenthesis straight x right parenthesis equals sin space 3 straight x
left parenthesis straight i right parenthesis space Since space sine space curve space is space continuous space
therefore space straight f left parenthesis straight x right parenthesis space is space continuous space function space in space open square brackets 0 comma space straight pi over 3 close square brackets
left parenthesis ii right parenthesis space straight f apostrophe left parenthesis straight x right parenthesis equals 3 space cos space 3 straight x comma space which space exists space in space open parentheses 0 comma space straight pi over 3 close parentheses
therefore space straight f left parenthesis straight x right parenthesis space is space derivable space in space open parentheses 0 comma space straight pi over 3 close parentheses
left parenthesis iii right parenthesis straight f left parenthesis 0 right parenthesis equals sin space 0 equals 0 comma space straight f open parentheses straight pi over 3 close parentheses equals sin space straight pi equals 0
therefore space straight f left parenthesis 0 right parenthesis equals straight f open parentheses straight pi over 3 close parentheses
therefore space straight f left parenthesis straight x right parenthesis space satisfies space all space the space conditions space of space Rolle apostrophe straight s space theorem. space
therefore space there space must space exist space at space least space one space value space straight c space of space straight x space such space that space straight f apostrophe left parenthesis straight c right parenthesis space equals space 0 space where
straight c element of space open parentheses 0 comma space straight pi over 3 close parentheses.
Now space straight f apostrophe left parenthesis straight c right parenthesis equals 3 space cos space 3 straight c
therefore space straight f apostrophe left parenthesis straight c right parenthesis equals 0 space gives space us space 3 space cos space 3 straight c equals 0 space straight i. straight i. comma space cos space 3 space straight c equals 0
therefore space space space 3 space straight c equals straight pi over 2 comma space fraction numerator 3 straight pi over denominator 2 end fraction comma space fraction numerator 5 straight pi over denominator 2 end fraction comma...
therefore space space space space space space straight c equals straight pi over 6 comma space fraction numerator 3 straight pi over denominator 2 end fraction comma space fraction numerator 5 straight pi over denominator 6 end fraction comma...
space Now space straight c equals straight pi over 6 space lies space in space open parentheses 0 comma space straight pi over 3 close parentheses
∴ Rolle's Theorem is verified.

Some More Questions From Continuity and Differentiability Chapter