答案为440根号2。完全不知道该怎么做。
设等比为q 其中q1,因为从小到大排列. 有 a13=2a1 a7=a1q^6
而a12=a1q^11 有 a1q^112a1 则 q^112
这个题会不会不全?
19.长方形,周长P,面积K,哪个一定对?
答案是2w^2-pw+2k=0.完全不知道该怎么做。
宽W,周长P,面积K ,则 长=K/W 周长=2=P
所以有2w^2-pw+2k=0
20.If x and y are positive integers such that x=8y+12,what is the greatest common divisor of x and y?
1) x=12u,where u is an integer
2) y=12z,where z is an integer
the key is D. How to deal with this kind of question.
由题知: x=4
由知: x=12u 则y=3k k is an integer. x=12 则x,y最大公因子不能确定.
由知: y=12z 则x=12 ,因此x,y的公因子是12。
这题我认为选B
21. If xy不等于0,is x/y 等于0吗?
1) x=-y 2)-x=y
答案是D。但我感觉1),2)这两个条件好象没有用。
由xy x0 且 y0, 因此x/y肯定不等于0。但是数据充分性的题,你不要管它有
没有用,意思是说如果成立,你能推出结论吗?如果能,就ok.所以选D
22.On Janes credit card account, the average daily balance for a 30-day billing cycle is the average of the daily balances at the end of each of the 30 days.At the beginning of a certain 30-day billing cycle,Janes credit card account had a balance of $600.Jane made a payment of $300 on the account during the billing cycle.If no other amounts were added to or subtracted from the account during the billing cycle, what was the average daily balance on Janes account for the billing cycle? 分页标题#e#
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