小弟不才 数学求教

lyuki

If n is positive integer and r is remainder when (n-1)(n+1) is divided by 24, what is the value of r?
(1)N is not divisible by 2
(2)N is not divisible by 3


In the xy-plane, at what two pts does the graph of y=(x+a)(x+b) intersect the x-axis?
(1)A+ b = -1
(2)The graph intersects the y-axis at (0, -6)


Z^n = 1, what is the value of z?
(1)N is a nonzero integer
(2)Z>0


At least 100 students at a certain high school study japanense. If 4 percent of the students at the school who study frech also study Japanese, do more students at the school study French than Japanese?
(1)16 students at the school study both French and Japanese
(2)10 percent of the students at the school who study Japanese also study French


A certain city with a population of 132,000 is to be divided into 11 voting districts and no district is to have a population that is more than 10 percent greater than the population of any other district. What is the minimum possible population that the least populated district could have?


谢谢。

另，SC错8个，CR错6个。。怎么提高？。。。

DarthWalker

半年没做数学，好像
C r=0
C (-3,0) (2,0)
C z=1
B
怎么没选项，我算了个10900

以上大概能对一半

clairesslc

1)c
2)c
3)b
4)c

DarthWalker

第3题如果仅有z>0，当n=0,z是无法确定的吧。。。

clairesslc

哦，对的。
任何数的0次方都是0是吧，我都忘了。

lyuki

最后题选项  10,700 10,800 10,900 11,000 11,100

lyuki

be divided的意思是可以整除吗？
第二题难道不是算b^2 - 4ac 吗？ 我算出来是>= 0 所以ab是啥都无所谓呀。。
n是 none zero integer 为什么（1）不充分？因为 +_ 1?
第四题totally不懂在说什么
第五题也不知道怎么算

DarthWalker

第一题不大会做，瞎代了几个数5,7,11,13最后r=0

第二题算和X轴交点的话就是能算出a,b的值就行了

我是这么觉得，±1，这道也是凭感觉的，具体证明不会

第四题你在纸上画一个venn图就清晰了

第五题好像应该人口最小的一个区设为x，然后其它10个选区的人口都是1.1x总共11x，这样总共132000=12x,x=11000,之前好像算错了

Gail小M

1  24=2 x2 x2 x3
1) if n is not divisible by 2, then n is odd, so both (n - 1) and (n + 1) are even. since every other even number is a multiple of 4, so the product (n - 1)(n + 1) contains one multiple of 2 and one multiple of 4, so it contains at least 2 x 2 x 2 = three 2's  
insuff.

2)if n is not divisible by 3, then exactly one of (n - 1) and (n + 1) is divisible by 3, because every thirdddd integer is divisible by 3. therefore, the product (n - 1)(n + 1) contains a 3 in its prime factorization. insuff.

conbine:sufficient

Gail小M

2  y= (x+a)(x+b) intersect the x-axis is equivalent to search the solutions of :
(x+a)(x+b) =0
<=> x^2 + (a+b)*x + a*b = 0
together  U can figure out the exact number of a,b  thus U can get the roots    C

3  two solutions to find the result as 1.
n can be zero (in this case z can be every integer except 0) or z can be 1 and -1 (if n is even).
1)  Z could be 1 and -1  insuff.

2)Z>0  n could be zero - thus Z: infinit solutions  insuff.

together suff- thus C