✔ 最佳答案
1.
x3y-10x2y2+25xy3
= xy (x2 - 10xy+25y2)
= xy (x-5y)2
2.
Question not complete. Missed out the number of years Peter old than his siter.
2009-02-05 23:45:45 補充：
Q 2. Peter is ( 7 ) years older than his sister. 9 years ago, he was twice as old as his sister
2009-02-05 23:45:54 補充：
Let P be the age of Peter now.
therefore the age of sister is P-7 now.
2009-02-05 23:45:58 補充：
9 years ago, Peter's age is P-9, and his sister's age is P-7-9 = P-16
He was twice as old as his sister 9 years ago, so
P-9 = 2 * (P-16) = 2P-32
P = 23
Therefore Peter's age is 23 years old now.
