PREP数学求助

candice90

1.If each term in the sum a1+a2+....+an is either 7 or 77, and the sum equals 350, which of the folowing is could be equal to n?
38  39  40 41 42 答案是40
2.IF the intergers a an n are greater than 1,and the product of the first 8 postive intergers is a mutiple of a^n, which is the value of a?
(1)a^n=64 (2)n=6  答案是B
3.if the xy-plane ,what is the y-intercept of line l
(1) the slope of the line is 3 times its y-intercept
(2)the x-intercept of the l is -1/3
答案是e 我觉得是C
4.n是5的倍数 n=(p^2)q,p和q都是质数 下面哪个是25的倍数 答案是(p^2)(q^2)

求解答啊！！

beihorse

7或77要加成350这样的，那数量肯定是10的倍数，7*10 = 70啊，其它的凑不成0啊，所以只可能40。

beihorse

4.n是5的倍数 n=(p^2)q,p和q都是质数 下面哪个是25的倍数 答案是(p^2)(q^2)
……


n是5的倍数 n=(p^2)q,p和q都是质数  

那P^2和Q中至少有一个是5的倍数，如果是P^2，因为是P是质数，那P一定是5，所以P^2就是25啦。
如果是Q是5，那Q^2就是25了。所以这两个p^2中q^2，肯定有一个是25。

beihorse

3.if the xy-plane ,what is the y-intercept of line l
(1) the slope of the line is 3 times its y-intercept
(2)the x-intercept of the l is -1/3
答案是e 我觉得是C

一起推不出来，不知道y-intercept

beihorse

2.IF the intergers a an n are greater than 1,and the product of the first 8 postive intergers is a mutiple of a^n, which is the value of a?
(1)a^n=64 (2)n=6  答案是B

8！里有 2 *4*8 = 2^6，这个最高了，N=6，那A肯定=2

candice90

2.IF the intergers a an n are greater than 1,and the product of the first 8 postive intergers is a mutiple of a^n, which is the value of a?
(1)a^n=64 (2)n=6  答案是B

8！里有 2 *4*8 = 2^6，这个最高了，N=6，那A肯定=2

-- by 会员 beihorse (2012/10/21 13:48:50)

谢谢你的及时回复 都明白了！！