Hi Melody...so I had another look at the question (thanks to your feedback) and tried to keep it simple.
So could the question be saying that the derivative of main function is a maximum and is equal to square root of same function (ie +/- values apply)...and therefore this is given and no need to prove it??!!
In that case I get the following for x (Word is terrible for writing power/equations so I hope there are no typos) - which agrees with book. Regards & thanks again
Hi Melody....thanks for your prompt reply.
This is the answer (no 10) offered in the book which also differs from your solution......heck (2nd time I met this circumstance)!
re 'do more to show it is a Max value' : I extracted 2 nd derivative which is a negative...thus pointing to a maximum value.
Thanks for your feedback & knowledge!