Bk5_Mock_6_E

Alex

2014-12-26 3:44 am

Suppose u varies inversely as v. When v = 6, u = 3.
(a)Express u in terms of v.
(b)If u > 2, find the range of the values of v.
(c)If v is increased by 25%, find the percentage change in u.
For part c, new value of u = 18/1.25v = 1/1.25u = 0.8u
I can't understand why the new value of u is caluclated in this way???!!

Given that z varies directly as and y varies inversely as x.
Which of the following is true?
A.z varies inversely as x.
B.z varies directly as x.
C.z varies inversely as the square of x.
D.z varies directly as the square of x.
(Answer is C)

Which of the following may be the graph of y = 2.5-x + 2? (-x is the power of 2.5)
A. https://www.flickr.com/photos/130230543@N06/16075975466/
B. https://www.flickr.com/photos/130230543@N06/16101029222/
C. https://www.flickr.com/photos/130230543@N06/16101031062/
D. https://www.flickr.com/photos/130230543@N06/15914335028/
(Answer is D)

回答 (1)

✔ 最佳答案

(a)
Since u varies inversely as v,
then u=k/v (where k is a non-zero constant)
sub v = 6, u = 3 into u=k/v
3=k/6 --> k=18
so u=18/v

(b)
since u>2
then 18/v > 2 (v is a non-zero positive constant)
so 9>v>0

(c)
Since v is increased by 25%
New v = (1+25%)v = 1.25v
New u = 18 / (1.25)v = 14.4 / v
% change = {(14.4/v) - (18/v)}/ (18/v) x 100% = -20%
So u is decreased by 20%

For M.C.Q. 2
y = 2.5-x + 2
We can modify it to y=(2/5)^x + 2
It is an exponential function
u can refer to https://www.google.com.hk/search?espv=2&biw=865&bih=493&tbm=isch&sa=1&q=y+%3D+a%5Ex&oq=y+%3D+a%5Ex&gs_l=img.3..0i19.47073.49692.0.49960.9.6.1.2.2.0.80.403.6.6.0.msedr...0...1c.1.60.img..0.9.409.bSEWxNPgn-g#facrc=_&imgdii=_&imgrc=p83XlBaFknj1pM%253A%3B0bvqFVt8irrraM%3Bhttp%253A%252F%252Fwww.pep.com.cn%252Fgzsxb%252Fjszx%252Fgzsxb%252Fjxsj%252Fbx1%252F201009%252FW020100905845919291558.jpg%3Bhttp%253A%252F%252Fwww.pep.com.cn%252Fgzsxb%252Fjszx%252Fgzsxb%252Fjxsj%252Fbx1%252F201009%252Ft20100905_871983.htm%3B453%3B370
(The R.H.S. Graph)
Since y=(2/5)^x will touch y axis at (0,1)
If we +2 to it , it will move upwards by 2 units ( y coordinates is increased by 2)
(i.e. (0,1)-->(0,3)) so D is the correct ans