***Disclaimer this is NOT a homework assignment nor is this going to be used for any reason other than personal understanding.***

The first equation in the picture above is to calculate the amount of Energy per ion pair in an ionic crystal. The book then takes the derivative of the equation to find the minimum amount of energy at r_{o} . The book then shows the derivative of the first equation and then they solved for r_{o} which is the second equation above. My question is: How did they take the derivative of the first equation? I have tried to take the derivative to get to the 2nd equation but after hours of failing to get the same result I turn to you. What steps did they take exactly? I'm not understanding where they are getting (1/(m-1)) from.

At least tell me what information is missing?

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