f(x)   = -x^2 -2x + 8
  
 This is a parabola  that turns "downward"  because thw leading coefficient is negative
  
 To find the x coordinate of the vertex...
  
 In the form    ax^2  + bx  + c
 The x coordinate of the vertex is    -b / [ 2a ]
 So....in our function,  b = (-2)   and  a = (-1)
 So...  -b / [ 2a]  = 2 / [ 2 * -1 ]   =  2 / -2   = -1
  
 To find the associated y value for the function....put  -1  back into it and evaluate
 - (-1)^2  -2(-1) + 8 =  -1 + 2 + 8  = 9
  
 So...(-1,9)  is the "high point"  of the function
  
 So....this function will increase  from  (-infinity, to -1)
  
 To find out where it tis positive on this interval...we can  find the  root on this side  [ where it crosses the x axis]
  
 So...we want to solve
  
 -x^2 - 2x  + 8  =0   multiply through by -1
  
 x^2 + 2x  - 8  =  0     factor
  
 (x + 4) (x - 2)  =0
  
 Set each factor to 0  and solve for x and we get   x = - 4   or  x  = 2
  
 So....this tells us that the function is positive and increasing from  
  
 -4 < x  <  -1    ⇒   B
  
 Here is the graph :  https://www.desmos.com/calculator/lmmko24qwo
  
  
  
  
 