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书书书因为O<A<rc,所以一工<A-工<扛,所以A-王=工,所以A=+. .................................... 6分
6 6 6 6 6 3
(2)设 6.ABC的外接圆半径为R,则R=l,a=2Rsin A=戎勹
由余弦定理得矿=片十c'2-2bccos—TC = (b+c)2 -3bc,即3=12-3bc,
3
所以杖=3,.................................................................................................................. 8分
........................................................................
所以6.ABC的面积为S=— 1 bcsin A=�- 10分
2 4
19. (1)(i)因为3个产品选择甲方案,2个产品选择乙方案,
1 3 3
所以5个产品全部测试合格的概率为P= (
2
) x(
4
)/ 2 =
12
9
8 '
. ............................................. 2分
(ii)4个产品测试合格分两种情况,
第一种情况,3个产品甲方案测试合格和1个产品乙方案测试合格,
3
此时概率为P1= (占) xcixfx(1一¾)=卢; .............................................................. 4分
第二种悄况,2个产品甲方案测试合格和2个产品乙方案测试合格,
此时概率为P2= C3 2x行 1 \ ) 2 X (1 - 了 1\ )x .,/ 勹 3\ ) 2 = 茂 27 '
所以4个产品测试合格的概率为P1+P2=
6
- 3
4
.+
1
- 2
2
7
8
=
1
- 3
2
3
8
................................................... 6分
(2)设选择甲方案测试的产品个数为n(n=0,1,2,3,4,5),则选择乙方案测试的产品个数为5-1/,并设通过
甲方案测试合格的产品个数为X,通过乙方案测试合格的产品个数为Y,
3
当n=O时,此时 所有产品均选择方案乙测试, 则Y~B(5,— 4),
所以E(X+Y)= E(Y) =5X— 3 =1 — 5 >3,符合题意;......,,....................................................... 8分
4 4
当n=5时,此时 所有产品均选择方案甲测试, 则X~B作,一 2) ,
所以E(X+Y)= E(X) =5X— 1 =— 5 <3,不符合题意; ......................................................... 10分
2 2
当n=l,2,3,4时,X~的分),Y-B(5-11,¾),
所以E(X+Y)= E(X)+E(Y)=—
2
1
.
'
1.1+.
3(5-
4
11) =一15-—
4
-
11
,
15-n
若使,ECX+Y)= 4 �3,解得咚;;;3,则n=l,2.3
综上,选择甲方案测试的产品个数为0,1,2,3时,测试合格的产品个数的期望不小于3. ............ 12分
20.(1)证明:?PA=PC,O为AC的中点,...PO上AC.
p
·:AB=BC,O为AC的中点,.· .AC上OB. ············································· 2分
·:po上AC,AC上OB,oBnPO=O,OB,PO仁平面PBO,
:.AC上平面PBO.··········································································· 4分
(2) 解:·:AB上BC,AB= BC= 2, PA= PB= PC= 2,,/z,0为AC的中点,AC=勾2, A c
:.BO=石,PO=顶,. . .PO'-+OB'= PB',:P. O上OB.
/3
又?AC上OB,AcnPO= O,AC,PO已平面PAC,
图1
【 “ 皖八 “ 高三开学.数学试卷参考答案 第4页(共6页)】 HD