1 if n is a multiple of 5 and n= p2q, where p and q are prim numbers, which of the following must be a multiple of 25?
p2; q2 ; pq; p2q2; p3q
the answer is p2q2,
why?
2 When a certain tree was first planted, it was 4 feet tall, and the height of the tree increased by a constant amount each year for the next 6 years. At the end of the 6th year, the tree was 1/5 taller than it was at the end of 4th year. By how many feet did the height of the tree increase each year?
3/10
2/5
1/2
2/3
6/5
难道不应该用a1+(n-1)d这个公式算么?怎么算不出答案呢?
我算法是4+5d=6/5(4+3d) d=4/7
1.因为 n 是5的倍数,n= p2q, p和q 是质数
所以 P或q是5,
如果p是5,那么p^2等于25, p^2q^2 是25的倍数.
如果q是5,那么q^2 等于25,p^2q^2 是25的倍数
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