some math JJ求助

redhat

130.一个数列，A1=2，A2=－3，A3=5，A4=－1，以后An=An－4，问数列的前97项和是多少？
[确认]74

131. 一辆车通过一个半圆隧道，隧道直径20 feet，车宽12 feet， 车高要低于最高限0.5feet ,问车高多少？
[确认]7.5


151.东东裂变。Triple in every 30min, what is the number of it after 4 hours divided by that in 2 hours?
[确认]81

-----题目的意思为何??

153.经纪人为客户服务，收取费用$10+1%* TOTAL AMOUNTS OF THE VALUME, 先买进了100share 50 per share, 后又卖出100share 65per share, 问卖出比买进多收的percent
[确认]25%

156.根号（2W）×四次方根号（2X）＝根号（2Y）×四次方根号（2Z），其中W＝4Y，且Y不等于0，问X in terms of Z?
[确认]Z/16


Thanks.

redhat

再请问一下...

131.如何求AB=8
Thanks a lot![em22]

redhat

thanks, tongxun and David0822. sorry, cause i'm gonna take G some time later. Here are some other questions. 161.z>x-y? (1)x,y,z是直角三角形三边 （2）z>x+y [确认]A --why is there any equation? 164.问|x|<1? 1) x/|x|< x 2) x < |x| [确认]C 171.set S 有240项，问第239项是多少 (1)除第一项外，每项都比前一项少4 (2)239项和第一项差952 [确认]D [em25][em25][em25]

redhat

Still confused.

[U]161、三角形的两边之和小于第三边。[/U]
I can't fiure this equation.


then x+y>z


设xyz是triangle的任三边,那么x+y>z对吗?
那如何推出z>x-y

而在171中若1>是不充份的那么答案怎么会是d，(没有提供第一项无法求出)?

TKU!