Given that the function FX = 3 ^ x + A / 3 ^ x is even, find the value of A

Given that the function FX = 3 ^ x + A / 3 ^ x is even, find the value of A

It is a decreasing function when the derivative is greater than the interval 0 and the increment value of the interval is less than 0
F'(X)= - 3×^ 2-6x + 9 BR>
The right side of the axis of symmetry is an increasing range. The left side is a small range
2, find the extremum point, the extremum point and the terminal value in [2,2] into the function, where the minimum value is the lowest value in the normal range