【纪念当年的帖子（2010）】Add Maths功课讨论区

Allmaths

get
-6q=p
4q^2=-9

square
puangenlun 发表于 15-2-2012 09:25 PM

    这个答案我喜欢。。。

lin96

题目是不是抄错？

是+9还是-9?
Allmaths 发表于 15-2-2012 09:02 PM

对不起！写错了，是+9...抱歉！
不过我还是不太明白...

-6q=p
4q^2=-9
p=+-9i
q=-+1.5i

是怎么得到p= +-9?

不过答案是对的

puangenlun

roots: q 2q
(x-q)(x-2q)=0
x^2-3qx+2q^2=0
2x^2-6qx+4q^2=0
compare with
2x^2+px+9=0
get
-6q=p
4q^2=9
p=+-9
q=-+1.5

lin96

这题我也不会

Given that the equation 5x^2 - 6x + k=0 has two equal roots. Find the values of k and the roots.

Allmaths

这题我也不会

Given that the equation 5x^2 - 6x + k=0 has two equal roots. Find the values of k an ...
lin96 发表于 16-2-2012 03:48 PM

    用discriminant。。。

b^2-4ac=(-6)^2-4(5)(k)=0
36-20k=0
k=9/5

lin96

用discriminant。。。

b^2-4ac=(-6)^2-4(5)(k)=0
36-20k=0
k=9/5
Allmaths 发表于 16-2-2012 04:16 PM

那root怎么找？答案是 k=1.8, x=0.6

Allmaths

那root怎么找？答案是 k=1.8, x=0.6
lin96 发表于 16-2-2012 04:24 PM

    substitute value of k回去equation。。

然后solve quadratic equation 就可以了

lin96

solving quadratic equation
----------------------------------

Given that x^2 +6x - 7= (x-p)(x+q)=0
find the values of p and q.

lin96

k(x)=4-3x
m(x)=  6/x-1           x not equal to 1

functions k and m are given  as shown. Find m^-1k(x)

Allmaths

solving quadratic equation
----------------------------------

Given that x^2 +6x - 7= (x-p)(x+q) ...
lin96 发表于 19-2-2012 03:47 PM

   x^2 +6x - 7=(x+7)(x-1)


compare with (x-p)(x+q),


p=1, q=7

Allmaths

k(x)=4-3x
m(x)=  6/x-1           x not equal to 1

functions k and m are given  as shown. Find m^ ...
lin96 发表于 19-2-2012 03:49 PM

    Let y=m^-1[k(x)]
then m(y)=k(x)

6/(y-1)=4-3x
y=[6/(4-3x)]+1
y=(10-3x)/(4-3x)
m^-1[k(x)]=(10-3x)/(4-3x)

lin96

Let y=m^-1[k(x)]
then m(y)=k(x)

6/(y-1)=4-3x
y=[6/(4-3x)]+1
y=(10-3x)/(4-3x)
m^-1[k ...
Allmaths 发表于 19-2-2012 05:12 PM

这个不是很明白，为什么y=[6/(4-3x)]+1？
然后为什么要let y =m^-1 [(k(x)]

Allmaths

这个不是很明白，为什么y=[6/(4-3x)]+1？
然后为什么要let y =m^-1 [(k(x)]
lin96 发表于 19-2-2012 06:15 PM

    因为Let y=m^-1 [(k(x)]， 你就能把function m inverse回去。。


所以就变成m(y)=k(x)， 更方便你做。。


如果你不Let y=m^-1 [(k(x)]， 你就要找inverse function m后才能算出答案。。会用更多时间。。


m(y)=k(x)
6/(y-1)=4-3x
y-1=6/(4-3x)
y=[6/(4-3x)]+1
y=(10-3x)/(4-3x)


之前你Let y=m^-1 [(k(x)]， 然后你又得到y=(10-3x)/(4-3x)， 所以你可以conclude y=m^-1 [(k(x)]=(10-3x)/(4-3x)

lin96

It is given that m and -2 are the roots of the quadratic equation 3x^2 + x - n=0, find the values of m and n

puangenlun

It is given that m and -2 are the roots of the quadratic equation 3x^2 + x - n=0,
find the values of m and n

m-2=-1/3
-2m=-n/3

lin96

1)if alfa and beta are the roots of the quadratic equation (2x-3)/8 = (3-2x)/5x , find the value of alfa^2 + beta^2

2)Given that one of the roots of the quadratic equation 5x^2-4x+r=0 is twice the other root, find the value or r.

请帮忙！明天就考add math了！ 感恩！

puangenlun

1)if alfa and beta are the roots of the quadratic equation (2x-3)/8 = (3-2x)/5x , find the value of alfa^2 + beta^2
(2x-3)/8 = (3-2x)/5x   ====>      ax^2+bx+c=0
x1+x2=-b/a
x1*x2=c/a
x1^2+x2^2=(x1+x2)^2-2*x1*x2

puangenlun

2. Given that one of the roots of the quadratic equation 5x^2-4x+r=0 is twice the other root, find the value or r.

x+2x=4/5
x*2x=r/5

乙劍真人

1)if alfa and beta are the roots of the quadratic equation (2x-3)/8 = (3-2x)/5x , find the value of  ...
lin96 发表于 7-3-2012 03:11 PM

http://cforum3.cari.com.my/viewthread.php?tid=1183356&rpid=42447351&ordertype=0&page=3#pid42447351

第 64 楼，work example 第五题.. 加油

lin96

simplifying algebraic expressions by using laws of indices

show that:
25^x-1 + 5^2x+1 = 5^2(x-1)(126)

这题不会做，谁可以帮帮忙？ 谢谢！