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Vector Algebra

Question
CBSEENMA12032896

For problem given below, verify that the given function (implicit or explicit) is a solution of the corresponding differential equation:
straight y space equals space straight x space sin space 3 straight x             :    fraction numerator straight d squared straight y over denominator dx squared end fraction plus 9 straight y minus 6 space cos space 3 straight x space equals space 0
         

Solution
The given differential equation is
                    straight y equals space straight x space sin space 3 straight x                       ...(1)
 rightwards double arrow         dy over dx space equals space straight x space cos 3 straight x space. space 3 space plus space sin space 3 straight x
and    fraction numerator straight d squared straight y over denominator dx squared end fraction equals 3 space open curly brackets straight x left parenthesis negative sin space 3 straight x space.3 right parenthesis plus cos space 3 straight x close curly brackets space plus space cos space 3 straight x. space 3
or     fraction numerator straight d squared straight y over denominator dx squared end fraction equals negative 9 space straight x space sin 3 straight x space plus space 6 space cos space 3 straight x
or      fraction numerator straight d squared straight y over denominator dx squared end fraction equals negative 9 straight y plus 6 space cos space 3 straight x                       open square brackets because space of space left parenthesis 1 right parenthesis close square brackets
or   fraction numerator straight d squared straight y over denominator dx squared end fraction plus 9 straight y minus 6 space cos space 3 straight x space equals space 0.
Hence the result.