Note:- If y = cos(ax) ; then dy/dx = -a*sin(ax)

If y = sin(ax) ; then dy/dx = a*cos(ax) ; where 'a' = constant

Now,

`h(t) = 10cos(t) - 15sin(t)`

`h'(t) = -10sin(t) - 15cos(t)`

`h''(t) = -10cos(t) + 15sin(t)`

`or, h''(t) = -h(t)`

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` `

Note:- If y = cos(ax) ; then dy/dx = -a*sin(ax)

If y = sin(ax) ; then dy/dx = a*cos(ax) ; where 'a' = constant

Now,

`h(t) = 10cos(t) - 15sin(t)`

`h'(t) = -10sin(t) - 15cos(t)`

`h''(t) = -10cos(t) + 15sin(t)`

`or, h''(t) = -h(t)`

``

` `