Question
If y = 500e7x + 600e-7x show that $\frac{{{d^2}y}}{{d{x^2}}} = 49y$.

Answer

Given: y = 500e7x + 600e-7x ...(i)

$\therefore \frac{{dy}}{{dx}} $ = 500e7x(7) + 600e-7x(-7) = 500(7)e7x - 600(7)e-7x

$\Rightarrow \frac{{{d^2}y}}{{d{x^2}}} $ = 500(7)e7x(7) - 600(7)e-7x(-7) = 500(49)e7x + 600(49){e-7x

$\Rightarrow \frac{{{d^2}y}}{{d{x^2}}} $ = 49[500e7x + 600e-7x]

= 49y [From eq. (i)]

$\Rightarrow \frac{{{d^2}y}}{{d{x^2}}} = 49y$ Hence proved.

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