1.the formula h=300t - 6t2次 gives the height, h, in meters, of a rocket t seconds after take-off. the maximum height reached by the rocket is 3750m. How long will it take the rocket to reach this maximum height?
2.A rectangular garden is fenced on three sides with a wall forming the fourth side. The total length of the fence is 30m. The area of the garden is 112m2次. Find the dimensions of the garden.
3.The edge of one cube is 2cm shorter than the edge of a second cube. The volumes of the two cubes differ by 386cm3次. Find the edge of the smaller cube.
maths
2010-09-04 5:44 am
回答 (2)
2010-09-04 6:47 am
✔ 最佳答案
1)For the maximum height reached by the rocket is 3750m
3750=300t-6t^2
t^2-50t+625=0
t=25
Hence, the time taken is 25s.
2)
Let the dimensions of the garden be x*y (x<y)
2x+y=30...(1)
xy=112...(2)
Sub (1) into (2),
x(30-2x)=112
-2x^2+30x-112=0
x=7 or x=8
So, when x=7, y=16 and when x=8, y=14
Hence, the dimensions are 7m*16m or 8m*14m
3)
Let the edge of the smaller cube be xcm and that of the larger one be (x+2)cm
Since the volumes of the two cubes differ by 386cm^3
(x+2)^3-x^3=386
[(x+2)-x][(x+2)^2+(x+2)(x)+x^2]=386
2(3x^2+6x+4)=386
3x^2+6x-189=0
x=7 or x=-9 (rejected)
Hence, the edge of the smaller cube is 7cm
2010-09-05 1:40 am
收錄日期: 2021-04-22 00:53:26
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20100903000051KK01467