Senior high school mathematical inequality proof: when a > 0, b > 0, 1 / AB + 1 / a (a-b) > = 4 / A ^ 2

Senior high school mathematical inequality proof: when a > 0, b > 0, 1 / AB + 1 / a (a-b) > = 4 / A ^ 2

1/(ab)+1/a(a-b)=(1/a)[1/b+1/(a-b)]=(1/a)[(a-b+b)/b(a-b)]=1/b(a-b)
Because B (a-b) ≤ [(B + a-b) / 2] &# 178; = A & # 178 / / 4
So 1 / b (a-b) ≥ 4 / A & # 178;
That is 1 / (AB) + 1 / a (a-b) ≥ 4 / A & # 178;
Note: consider that the condition should be a > b > 0