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A difficulty in understanding 2 examples in Petrovic.



Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)
Announcing the arrival of Valued Associate #679: Cesar Manara
Unicorn Meta Zoo #1: Why another podcast?A difficulty in understanding the solution of Exam GRE 0568 Q31.A difficulty in understanding a use of Cauchy Schwartz inequality.Difficulty(3) in understanding the completeness of $l_2.$A difficulty in understanding theorem 4.2 in Israel Gohberg.A difficulty in understanding Theorem 4.3 in Israel Gohberg.A difficulty in understanding a proof for L'Hospital's rule (in Petrovic)A difficulty in understanding the proof of 7.2.3 Petrovic.A difficulty in understanding a statement in example 10.6.6 Petrovic.A difficulty in understanding a step in the proof of Thm. 11.5.6 in Petrovic.A difficulty in understanding multivariable Fermat theorem proof.










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$begingroup$


Those are the two examples:



enter image description here



But it is not clear for me how example 1 shows if $f$ is injective then $Df$ is injective, could anyone explain for me how this is shown please?



Also in example 2:



1-It is not clear for me why he wrote in DF(a) an $x$, what is this $x$ multiplied by the given matrix, from where it comes?



2-Also I do not understand how he proved that the injectivity of the derivatives implies the injectivity of $**f**$? more precisely I do not understand why $DF(a)(x_1) = DF(a)(x_2)$ iff $x_1 = x_2$ and also what is the importance of saying $**f**(t_1) = **f**(t_2)$ implies $t_1 = t_2$, is there a relation between $t_1$ and $x_1$, and $t_2$ and $x_2$ ?



3-It is not clear for me also why the inverse is incorrect i.e. injectivity of $f$ does not imply injectivity of the derivative, could anyone clarify this for me please?



Could anyone clarify this points for me please?










share|cite|improve this question











$endgroup$
















    0












    $begingroup$


    Those are the two examples:



    enter image description here



    But it is not clear for me how example 1 shows if $f$ is injective then $Df$ is injective, could anyone explain for me how this is shown please?



    Also in example 2:



    1-It is not clear for me why he wrote in DF(a) an $x$, what is this $x$ multiplied by the given matrix, from where it comes?



    2-Also I do not understand how he proved that the injectivity of the derivatives implies the injectivity of $**f**$? more precisely I do not understand why $DF(a)(x_1) = DF(a)(x_2)$ iff $x_1 = x_2$ and also what is the importance of saying $**f**(t_1) = **f**(t_2)$ implies $t_1 = t_2$, is there a relation between $t_1$ and $x_1$, and $t_2$ and $x_2$ ?



    3-It is not clear for me also why the inverse is incorrect i.e. injectivity of $f$ does not imply injectivity of the derivative, could anyone clarify this for me please?



    Could anyone clarify this points for me please?










    share|cite|improve this question











    $endgroup$














      0












      0








      0





      $begingroup$


      Those are the two examples:



      enter image description here



      But it is not clear for me how example 1 shows if $f$ is injective then $Df$ is injective, could anyone explain for me how this is shown please?



      Also in example 2:



      1-It is not clear for me why he wrote in DF(a) an $x$, what is this $x$ multiplied by the given matrix, from where it comes?



      2-Also I do not understand how he proved that the injectivity of the derivatives implies the injectivity of $**f**$? more precisely I do not understand why $DF(a)(x_1) = DF(a)(x_2)$ iff $x_1 = x_2$ and also what is the importance of saying $**f**(t_1) = **f**(t_2)$ implies $t_1 = t_2$, is there a relation between $t_1$ and $x_1$, and $t_2$ and $x_2$ ?



      3-It is not clear for me also why the inverse is incorrect i.e. injectivity of $f$ does not imply injectivity of the derivative, could anyone clarify this for me please?



      Could anyone clarify this points for me please?










      share|cite|improve this question











      $endgroup$




      Those are the two examples:



      enter image description here



      But it is not clear for me how example 1 shows if $f$ is injective then $Df$ is injective, could anyone explain for me how this is shown please?



      Also in example 2:



      1-It is not clear for me why he wrote in DF(a) an $x$, what is this $x$ multiplied by the given matrix, from where it comes?



      2-Also I do not understand how he proved that the injectivity of the derivatives implies the injectivity of $**f**$? more precisely I do not understand why $DF(a)(x_1) = DF(a)(x_2)$ iff $x_1 = x_2$ and also what is the importance of saying $**f**(t_1) = **f**(t_2)$ implies $t_1 = t_2$, is there a relation between $t_1$ and $x_1$, and $t_2$ and $x_2$ ?



      3-It is not clear for me also why the inverse is incorrect i.e. injectivity of $f$ does not imply injectivity of the derivative, could anyone clarify this for me please?



      Could anyone clarify this points for me please?







      real-analysis calculus analysis multivariable-calculus implicit-function-theorem






      share|cite|improve this question















      share|cite|improve this question













      share|cite|improve this question




      share|cite|improve this question








      edited Apr 1 at 1:20







      hopefully

















      asked Mar 31 at 22:48









      hopefullyhopefully

      190215




      190215




















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