初中数学题
\u521d\u4e2d\u6570\u5b66\u9898\u8bc1\u660e\uff1a\uff081\uff09\u8fde\u63a5AD\uff0e
\u2235AB\u662f\u2299O\u7684\u76f4\u5f84\uff0c
\u2234\u2220ADB=\u2220AEB=90\u00b0\uff0c
\u2235AB=AC\uff0c
\u2234DC=DB\uff0e
\u2235OA=OB\uff0c
\u2234OD\u2016AC\uff0e
\u2234\u2220OFB=\u2220AEB=90\u00b0\uff0c
\u2234OD\u22a5BE\uff0e
\u89e3\uff1a\uff082\uff09\u8bbeAE=x\uff0c
\u7531\uff081\uff09\u53ef\u5f97\u22201=\u22202\uff0c
\u2234BD=ED= 52\uff0c
\u2235OD\u22a5EB\uff0c
\u2234FE=FB\uff0e
\u2234OF= 1/2AE= 1/2x\uff0cDF=OD-OF= 5/4-1/2x\uff0e
\u5728Rt\u25b3DFB\u4e2d\uff0c BF\u5e73\u65b9=DB\u5e73\u65b9-DF\u5e73\u65b9=(\u6839\u53f75/2)\u5e73\u65b9-(5/4-1/2x)\u5e73\u65b9\uff1b
\u5728Rt\u25b3OFB\u4e2d\uff0c BF\u5e73\u65b9=OB\u5e73\u65b9-OF\u5e73\u65b9=(5/4)\u5e73\u65b9-(1/2x)\u5e73\u65b9\uff1b
\u2234 (\u6839\u53f75/2\u5e73\u65b9)-(5/4-1/2x)\u5e73\u65b9= (5/4)\u5e73\u65b9-(1/2x)\u5e73\u65b9\uff0e
\u89e3\u5f97 x=3/2\uff0c\u5373 AE=3/2\uff0e
1.=(4-a²)/a-2\u00f7 (a²+6a+9)\u00f72(a+3)
=-2(a+2)(a+3)/(a²+6a+9)
=-2(a+2)/(a+3)
\u5f53a=-2\u65f6 \u539f\u5f0f=0
2.c
3.x1²\uff0b2x1x2+x2²\uff1d24+2x1x2
(x1+x2)²=24+k+1
6²-25=k
k=11
4.kx\uff0d1\uff1d2x
kx-2x=1
(k-2)x=1
\u5f53k\uff1e2\u65f6 \u65b9\u7a0b\u6709\u6b63\u5b9e\u6570\u89e3
5. \u8bbe\u539f\u6765\u8fb9\u957f\u4e3axcm
\uff08x+1\uff09(x+2)=x²+14
3x=12
x=4
6.2x\uff1c4
x\uff1c2(a\uff0d1\uff09x\uff1ca\uff0b5
\u82e5a\uff1e1 \u5219x\uff1c\uff08a+5\uff09/(a-1)
\uff08a+5\uff09/(a-1)\uff1c2
a\uff1e7
\u82e5a\uff1c1 \u5219x\uff1c\uff08a+5\uff09/(a-1)
\uff08a+5\uff09/(a-1)\uff1e2
a\uff1c7
\u54b3\u54b3- -lz\u591a\u7ed9\u70b9\u5206\u628a \uff0cme\u53ef\u662f\u4e00\u4e2a\u5b57\u4e00\u4e2a\u5b57\u6253\u51fa\u6765\u7684
2 (1+2=3)√
3 (1+3=4)
2 1 (2+1=3)√
2 (2+2=4)
3 (2+3=5)√
3 1 (3+1=4)
2 (3+2=5)√
3 (3+3=6)
5 1 (5+1=6)
2 (5+2=7)√
3 (5+3=8)
P(欢欢获胜)= 5\12 P(乐乐获胜)=7\12
∵P(欢欢获胜)<P(乐乐获胜)
∴游戏不公平,欢欢获胜机会小。
解:方法一画树状图
由上图可知,所有等可能的结果共有12种,指针所指的两个数字之和为奇数的结
果有5种.
∴P(和为奇数)=5/12
∴欢欢获胜的概率是5/12.
方法二列表如下:
由上表可知,所有等可能的结果共有12种,指针所指的两个数字之和为奇数的结
果有7种.
∴P(和为奇数)=5/12;
∴欢欢获胜的概率是5/12.
(2)∵P(和为奇数)=5/12,
∴P(和为偶数)=7/12,
∵P(和为奇数)≠P(和为偶数)
∴这个游戏规则对双方是不公平的.
1 123
2123
3123
5123
共12种获胜为5\12 不公平p=5\12小于6\12
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