[DSE 2019] 你地溫 數學 又溫成點呢? [2]

1001 回覆
37 Like 18 Dislike
2018-12-05 00:30:28
想問cii 點用a part個prove 我淨係識otherwise
唔知佢其實想學生點做 諗左好耐
2018-12-05 00:33:09
上下乘cos^2變咗做ci嗰舊嘢
ci - b 嗰舊嘢係可以用簡單substitution嚟做
2018-12-05 00:36:25
但好似冇用過
in (x)fx=a/x infx個舊嘢?
2018-12-05 00:37:02
2018-12-05 00:38:29
咁將ci嗰舊嘢用a嘅結果將個分子變到無x
就可以用到b嘅結果啦

差唔多啦,做到就得
2018-12-05 00:45:23
屌 sorry大家 我on9左
我以為b part同c part左邊舊嘢係一樣
我一直係到諗啲sin cos 邊個當x塞
2018-12-05 00:45:54
f(x)=(2x^2+px+1)g(x)=(3x^2+2x+q)h(x) for some polynomial g and h
h(x) = (2x^2+px+1)g(x) / (3x^2+2x+q)
since G.C.D.(2x^2+px+1,3x^2+2x+q) = 1, g(x) is divisible by (3x^2+2x+q) .
Note that 4 = degree of f = degree of g +2, so degree of g = 2
Hence, g(x) = k (3x^2+2x+q) for some non-zero constant k.
so f(x) = k(2x^2+px+1)*(3x^2+2x+q)
comparing the leading coefficient, we have k = 2
2018-12-05 00:52:34
第二行h(x)做主項嗰句其實唔寫好啲
唔使煩嗰啲domain問題
2018-12-05 01:30:11
since G.C.D.(2x^2+px+1,3x^2+2x+q) = 1, g(x) is divisible by (3x^2+2x+q) .
2018-12-05 09:24:22
好似要有euldiean algorithm先証到 當我無講過
2018-12-05 11:17:48
euclidean algorithm 算 number theory 唔算 abstract algebra
2018-12-05 14:28:51
求救 how many real roots does the equation x^5+2x^3+3x-6=0 have
2018-12-05 14:30:03
你試下搵佢啲turning points先
呢隻D完唔難solve
2018-12-05 14:31:52
我試下先 係咪一開始都唔洗抽(x-1)?
2018-12-05 14:32:40
唔使
就咁D
2018-12-05 14:38:37
Sorry會考巴 d完一次大過0之後冇頭緒
2018-12-05 14:40:04
咁即係條曲線不斷向上升
得一個real root
2018-12-05 15:09:59
啲 non-constant term 全部都 strictly increasing 喎
2018-12-05 19:31:54
f'(x)=5x^4+6x^2+3>0 for all real x
f is strictly increasing.
note that f(x) <f(1) =0 for x <1 and
f(x) >f(1) =0 for x >1
f has only one real root
2018-12-05 19:33:54
其實你知佢strictly increasing同埋個degree 係odd no. 應該都夠,唔洗特登揾個root出來
2018-12-07 12:24:17

數學求救
下面果個係答案黎
LHS 唔係應該= F'(4)咩?
如果係咁既話 F'(4) = f(4)/(2*4^(1/2))=1/2?
諗左勁耐都唔明
2018-12-07 12:35:32
Chain rule
F'(4)=f(sqrt(4))*(1/2)*(4^(-1/2))
=f(2)/4=3/4
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