11/08/16 05:26:39.15
>>498
次に
f(A^3,1/A,1/A,1/A) ≧ 25/４, (A≧1)
を示そう。
f(A^3,1/A,1/A,1/A) - 25/4
= 1/A^3 + 3A + 9A/(A^4 +3) - 25/4
= 3(A-1)^2･{A^6 -(1/12)A^5 -(7/6)A^4 -(9/4)A^3 +3A^2 +2A +1}/{A^3(A^4 +3)}
= 3(A-1)^2･g(A)/{A^3(A^4 +3)}
≧ 0,
∵ g(A) = A^6 -(1/12)A^5 -(7/6)A^4 -(9/4)A^3 +3A^2 +2A +1
= {A^3 -(1/24)A^2 -(673/1152)A -(31777/27648)}^2 + 2.56293026A^2 +0.657105936A -0.3209864
= {A^3 -(1/24)A^2 -(673/1152)A -(31777/27648)}^2 + 2.56293026(A-1)^2 +5.782966457A +2.899049797
> 0.
難しくない。>>503