Let's define it by parabola.

y？ =8x

∴? Align l:x=-2,? Focus f (2,0)

The straight line y=k(x+2)? (k>0) Constant Intersection Point P (-2,0)

As shown in the figure, A and B are AM⊥l in M and BN⊥l in N, respectively.

If |FA|=2|FB|, then |AM|=2|BN|,

Point b is the midpoint of AP, connecting OB,

∴? |OB|=( 1/2)|AF|，

∴|OB|=|BF|，

The abscissa of point b is 1,

Substitute it into the parabolic equation to get B( 1, 2√2).

∴? K = K(PB)=(2√2-0)/( 1+2)= 2√2/3