作业帮12 13题求解答.必最佳.
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12 13题求解答.必最佳.
再答： F(X)=1/3 aX3 1/2aX2-2aX 2a 1 F’(X)=aX^2 aX-2a=a(x 2)(x-1) 在x=-2，x=1处有极点， 且f(-2)=16a/3 1,f(1)=5a/6 1, f(0)=2a 1 1.a＞0时, x＜-2时,f(x)不过第四象限; -2＜x＜0时,f(x)不过第四象限; 0＜x＜1时,f'(x)＜0,f(x)递减,5a/6 1＜f(x)＜2a 1,因a＞0,f(x)不过第四象限; x＞1时,f'(x)＞0,f(x)递增,f(x)＞5a/6 1,因a＞0,f(x)不过第四象限. 2.a＜0时, x＜-2时,x在二三象限,f'(x)＜0,,f(x)递减,f(x)＞16a/3 1; -2＜x＜0时,x在二三象限,f'(x)＞0,,f(x)递增,16a/3 1＜f(x)＜2a 1; 0＜x＜1时,x在一四象限,f'(x)＞0,f(x)递增,2a 1＜f(x)＜5a/6 1,f(x); x＞1时,x在一四象限,f'(x)＜0,f(x)递减,f(x)＜5a/6 1, 所以a＜0, x＜0,x在二三象限,16a/3 1＜f(x)＜2a 1,f(x)过二三象限的充要条件是16a/3 1＜0,2a 1＞0,-1/2＜a＜-13/16 x＞0,x在一四象限,2a 1＜f(x)＜5a/6 1,f(x)过一四象限的充要条件是5a/6 1＞0,2a 1＜0 ,-6/5＜a＜-1/2 snyhs | 2009-06-04 29 0再答： F(X)=1/3 aX3 1/2aX2-2aX 2a 1 F’(X)=aX^2 aX-2a=a(x 2)(x-1) 在x=-2，x=1处有极点， 且f(-2)=16a/3 1,f(1)=5a/6 1, f(0)=2a 1 1.a＞0时, x＜-2时,f(x)不过第四象限; -2＜x＜0时,f(x)不过第四象限; 0＜x＜1时,f'(x)＜0,f(x)递减,5a/6 1＜f(x)＜2a 1,因a＞0,f(x)不过第四象限; x＞1时,f'(x)＞0,f(x)递增,f(x)＞5a/6 1,因a＞0,f(x)不过第四象限. 2.a＜0时, x＜-2时,x在二三象限,f'(x)＜0,,f(x)递减,f(x)＞16a/3 1; -2＜x＜0时,x在二三象限,f'(x)＞0,,f(x)递增,16a/3 1＜f(x)＜2a 1; 0＜x＜1时,x在一四象限,f'(x)＞0,f(x)递增,2a 1＜f(x)＜5a/6 1,f(x); x＞1时,x在一四象限,f'(x)＜0,f(x)递减,f(x)＜5a/6 1, 所以a＜0, x＜0,x在二三象限,16a/3 1＜f(x)＜2a 1,f(x)过二三象限的充要条件是16a/3 1＜0,2a 1＞0,-1/2＜a＜-13/16 x＞0,x在一四象限,2a 1＜f(x)＜5a/6 1,f(x)过一四象限的充要条件是5a/6 1＞0,2a 1＜0 ,-6/5＜a＜-1/2 snyhs | 2009-06-04 29 0