JEE Main & Advanced Mathematics Differential Equations Question Bank Variable Separable type differential equations

  • question_answer
    The solution of the differential equation \[\cos y\log (\sec x+\tan x)dx=\cos x\log (\sec y+\tan y)dy\] is [AI CBSE 1990]

    A)                 \[{{\sec }^{2}}x+{{\sec }^{2}}y=c\]           

    B)                 \[\sec x+\sec y=c\]

    C)                 \[\sec x-\sec y=c\] 

    D)                 None of these

    Correct Answer: D

    Solution :

                       \[\cos y\log (\sec \,\,x+\tan x)dx=\cos x\log (\sec y+\tan y)dy\]                    Þ \[\int_{{}}^{{}}{\sec y\log (\sec y+\tan y)dy}\]                                 \[=\int_{{}}^{{}}{\sec x\log (\sec x+\tan x)dx}\]                    Put \[\log (\sec x+\tan x)=t\]and\[\log (\sec y+\tan y)=z\]                                 \[\frac{{{[\log (\sec x+\tan x)]}^{2}}}{2}=\frac{{{[\log (\sec y+\tan y)]}^{2}}}{2}+c\].    


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