Xét tính đơn điệu hàm số y=1+4x-x^2

The graph of the function f(x) = (x + 2)(x + 6) is shown below. which statement about the function is true? the function is positive for all real values of x where x > –4. the function is negative for all real values of x where –6 < x < –2. the function is positive for all real values of x where x < –6 or x > –3. the function is negative for all real values of x where x < –2.