Find the minimum and maximum values of x and the values of f(x) at these points if:
f(x) = 10.9sin(0.7x)+2.1cos(0.7x)
The range is (-.27,8.7)
I don't know/think there are any
The Attempt at a Solution
I found f'(x) = 7.43cos(0.7x)-1.47sin(0.7x) = 0 and simplified to tan(0.7x) = 7.43/1.47. so arctan(7.43/1.47) = 0.7x or so I thought, but that doesn't seem to be the case as I can't find a value of x within the range.
Please give me some kind of advice, any help is welcome, thank you in advance.