11、x^2+x-60,问:x=?
x是自然数;
-2
【答案】A
【思路】
x^2+x-6 -3与2是该一元二次方程的两个根,也就是该函数图像与X轴交于和。x^2+x-60,则-3
x为自然数,则与上述x值域有交集,得出x为小于2的自然数,x=1。充分;
-2
12、数列{7, 6, 9, 10, 4}加入3,7,12,哪个使得新的数列median=mean?
I. 3
II. 7
III. 12
【答案】3和12
【思路】
数列加3,新数列为{3,4,6,7, 9,10}, median=/2=6.5,mean=39/2=6.5, I可以;
数列加7,新数列为{4,6,7, 7,9,10}, median=7,mean=43/67.2, II不可以;
数列加12,新数列为{4,6,7, 9,10,12}, median=/2=8,mean=48/6=8, III可以。
13、-3
【答案】|x+1|2
【思路】-3
14、A1=2, A2=3, A3=A1A2, A4=A1A2A3, ,若An=t,那么An+2=?
【答案】t^4
【思路】
根据条件可得:A=A1A2A3.AnA; A=A1A2A3.AAn;
An=A1A2A3.A=t A=An^2, 同理可得A =A^2;
代入则有:A =An^4=t^4
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