The two foci F1, F2 and P of hyperbola x2 / 4-y2 / B2 = 1 are the points on the hyperbola, Pf1, F1F2 and PF2 form an arithmetic sequence, and op = 5, then B ^ 2 =?

The two foci F1, F2 and P of hyperbola x2 / 4-y2 / B2 = 1 are the points on the hyperbola, Pf1, F1F2 and PF2 form an arithmetic sequence, and op = 5, then B ^ 2 =?

Let Pf1 = m, PF2 = M-4, then M + M-4 = 4C, and (2op) ^ 2 + F1F2 ^ 2 = 2 (m ^ 2 + (M-4) ^ 2)
So 100 + (m-2) ^ 2 = 2m ^ 2 + 2 (M-4) ^ 2, the solution is 3M ^ 2-12m-72 = 0, M = 2 + 2, root 7
b^2=c^2-4=(0.5m-1)^2-4=3