need help

A rectangle is inscribed with its base on the x-axis and its upper corners on the parabola y = 12 - x2 . Find the dimensions of such rectangle with the maximum possible area.Given the function f(x) = x4 - 6x2 : a. Calculate f (x) and use it to determine intervals where the function is increasing, intervals where it is decreasing, and the local extrema (if any). b. Calculate f"(x) and use it to determine intervals where the function is concave upward, intervals where the function is concave downward, and the inflection points (if any)