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# c3 differentiation watch

1. given y= sinx + cosx show d(^2)y/dx + y = 0
2. (Original post by yaaasminb)
given y= sinx + cosx show d(^2)y/dx + y = 0
Tried any approaches to this?
3. Alright first try working out dy/dx. Once you have that, differentiate that again to get d2y/dx2. Since you have both y and now d2y/dx2, you can put them both into the equation its asking for: d2y/dx2 + y. Simplify it and you should get your answer.

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Updated: November 13, 2017
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