→ QQLeopard : 謝謝你：） 10/07 01:33
※ 引述《QQLeopard (QQ)》之銘言：
: 1.
: https://i.imgur.com/YQvH1pA.jpg
f(x) = ax^2 + bx = a(x + b/(2a))^2 - (b^2)/(4a)
a =/= 0
f(x - 106)有最大值 = 1
=> a < 0，4a + b^2 = 0
(4 + t + 2 - t)/2 = -b/2a => 6a + b = 0
=> 4a + 36a^2 = 0
=> a = -1/9，b = 2/3
=> f(x) = -(1/9)x^2 + (2/3)x
: 2.
: https://i.imgur.com/Wr7MYOV.jpg
y(x) = x^2 + kx + a > 2x + 1 for all k, x
=> x^2 + (k - 2)x + (a - 1) > 0 for all k, x
=> (k - 2)^2 - 4(a - 1) < 0 for all k
=> k^2 - 4k + 4(2 - a) < 0 for all k
應該不存在這種a滿足all k的情況
: 3.
: https://i.imgur.com/sAD6Vic.jpg
: 有請神人求解謝謝你們：）
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