Also without a calculator you know 4^1 = 4 and 4^2 = 16 so x is going to be between 1 and 2 so 1.585 sounds sensible. A useful check if you don't have a calculator
hey man is turning point the same as stationary point?
Like TenOfThem said, for the most part yes, turning points are when you have minimums and maximums where the gradient changes at the stationary point, however this isn't always the case such as points of inflection.