1.數列3,9,27,81,243,...的第n項是________
2.若X:Y=2:5及Y:Z=3:2,則X:Y:Z=________
3.若(5-2x)(x+4)-2x+7)+k中的常數項等於10,求ｋ的值
MAths(10點)
2007-08-24 2:03 am
回答 (4)
2007-08-24 2:09 am
✔ 最佳答案
3^n----------3^1=3,3^2=9,3^3=27,3^4=81,3^5=243..............................................
x:y=2:5=6:15
x:y=2:3=10:15
so x:y:z=6:15:10
...............................................
(5-2x)(x+4)-2x+7+k
=5x+20-2x^2-8x-2x+7+k
=-2x^2-5x+27+k
so 27+k=10
k=-17
2007-08-24 2:27 am
Question1
3,3x3,3x3x3,3x3x3x3...........
=3的一次方,3的二次方,3的三次方.........
So, 第n項是3的n次方
Question2
X:Y=2:5
Y:Z=3:2
Y:Z=(3x5:2x5)
Y:Z=15:10
X:Y=2:5
X:Y=2x3:5x3
X:Y=6:15
Y:Z=15:10
X:Y:Z=6:15:10
3,3x3,3x3x3,3x3x3x3...........
=3的一次方,3的二次方,3的三次方.........
So, 第n項是3的n次方
Question2
X:Y=2:5
Y:Z=3:2
Y:Z=(3x5:2x5)
Y:Z=15:10
X:Y=2:5
X:Y=2x3:5x3
X:Y=6:15
Y:Z=15:10
X:Y:Z=6:15:10
2007-08-24 2:12 am
（2）是6;15:10
2007-08-24 2:11 am
2.x:y:z=6:15:10
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