Ok. That's looks right (I'm trusting you here ). So we need to differentiate both sides with respect to x. To differentiate the RHS we need to use the product rule. So we have dx2d2y=dxd(cosx)dzdy+cosxdxd(dzdy). I assume your trouble is differentiating the second term. dxd(dzdy)=dxdzdzd(dzdy)=dxdzdz2d2y. From the substitution you have been given you should be able to find an expression for dz/dx. Hope this helps.
Ok. That's looks right (I'm trusting you here ). So we need to differentiate both sides with respect to x. To differentiate the RHS we need to use the product rule. So we have dx2d2y=dxd(cosx)dzdy+cosxdxd(dzdy). I assume your trouble is differentiating the second term. dxd(dzdy)=dxdzdzd(dzdy)=dxdzdz2d2y. From the substitution you have been given you should be able to find an expression for dz/dx. Hope this helps.
Thank you so much! Do you mind if over the next couple of days I send any more questions I get stuck on to you . Your explanation was very helpful
m1 im confused about part a-how is reaction force of the lift equal to the downward forces of albert and bella, surely you can only use the masses for the downwards force