Confused with this sum

[ShaheenNazar]

If y = e^x cosx, find d^2y/dx^2. If the calculations are done step by step, it would be great!

 

[Deleted member 4993]

If y = e^x cosx, find d^2y/dx^2. If the calculations are done step by step, it would be great!

Your subject-line says you are "confused with this sum". I do not see any indication of "sum"

For the problem stated, you should know that:

$\displaystyle \frac{d}{dx}e^x = e^x$

continue...

 

[HallsofIvy]

Subhotosh Kahn, in countries heavily influenced by Britain it is not unusual to use the term "sum" to mean any mathematics problem.

Shaheen Nazar, are you taking a Calculus class? This is a Calculus problem and before you could be expected to do it, you should have learned a number of things:
1) that the derivative of $\displaystyle e^x$ is $\displaystyle e^x$.
2) that the derivative of cos(x) is -sin(x).
3) that the derivative of sin(x) is cos(x).
3) the "product rule- $\displaystyle \frac{d(fg)}{dx}= \frac{df}{dx}g+ f\frac{dg}{dx}$.
4) that $\displaystyle \frac{d^2f}{dx}$ means that you differentiate twice.