It has been a long time since I've had to do derivatives so I'm rusty.

show that where 'k' is constant.

I get :

and

so if I multiply the second order derivative (U_xx) by 'k' then this should be correct?

I just want to make sure that since I'm doing partial derivatives with respect to x for the last 2 that I can ignore the because it is all a cosntant. And when I do the derivative of I only need to pull the 'n' out and change it to cos(nx). Also, for the first derivative with respect to 't' I am taking the '1' exponent off of 't' and bringing it forward.

Last semester was 100% integrals and I feel like I have to relearn the first semester all over. Thanks for the help.

Also, just notices that my doesnt work. Anyone able to tell me how to get two sub x's in a row. Figured parathese would work, guess not.