This discussion is closed.
hihihihi
Badges: 0
Rep:
?
#1
Report Thread starter 15 years ago
#1
if u have a modulus expression say

l 3x+5 l = l 5x l

do you have to square both sides to solve, or do you just treat the mod bit as brackets


or wqhat if you have one\side with a modulus bit
eg solve for x, in terms of a:
3a = l x-(4x+a) l +a

i get x= 2a(1-a)/(1-4a)

could someone post some more examples with solutions of different types of mod equation questions
0
IntegralAnomaly
Badges: 0
Rep:
?
#2
Report 15 years ago
#2
(Original post by hihihihi)
if u have a modulus expression say

l 3x+5 l = l 5x l

do you have to square both sides to solve, or do you just treat the mod bit as brackets


or wqhat if you have one\side with a modulus bit
eg solve for x, in terms of a:
3a = l x-(4x+a) l +a

i get x= 2a(1-a)/(1-4a)

could someone post some more examples with solutions of different types of mod equation questions
you can square them or draw a graph,depends on how much algebra u want to do..............
0
Bhaal85
Badges: 9
Rep:
?
#3
Report 15 years ago
#3
(Original post by hihihihi)
if u have a modulus expression say

l 3x+5 l = l 5x l

do you have to square both sides to solve, or do you just treat the mod bit as brackets


or wqhat if you have one\side with a modulus bit
eg solve for x, in terms of a:
3a = l x-(4x+a) l +a

i get x= 2a(1-a)/(1-4a)

could someone post some more examples with solutions of different types of mod equation questions
² ³ ± ÷ ° √ ∂ ∞ ≈ ≠ ≡ ≥ ≤ ø Ø ½ ¼ « » µ π

l 3x+5 l = l 5x l
Square both sides:
9x²+30x+25=25x²
16x²-30x-25=0
(8x+5)(2x-5)
Therefore solutions are:
x=-5/8 or x=5/2

3a = l x-(4x+a) l +a
2a = l x-(4x+a) l
±2a = x-(4x+a) therefore:

3a+3x=0
OR
-a+3x=0
0
Silly Sally
Badges: 0
Rep:
?
#4
Report 15 years ago
#4
(Original post by Bhaal85)
² ³ ± ÷ ° √ ∂ ∞ ≈ ≠ ≡ ≥ ≤ ø Ø ½ ¼ « » µ π


3a = l x-(4x+a) l +a
2a = l x-(4x+a) l
±2a = x-(4x+a) therefore:

3a+3x=0
OR
-a+3x=0
I don't understand the ±2 in the bold bit??? Where did that come from
0
Bhaal85
Badges: 9
Rep:
?
#5
Report 15 years ago
#5
(Original post by Silly Sally)
I don't understand the ±2 in the bold bit??? Where did that come from
The modulus can be switched, e.g.

a = l x l is the same as saying:
±a = x
0
Silly Sally
Badges: 0
Rep:
?
#6
Report 15 years ago
#6
(Original post by Bhaal85)
The modulus can be switched, e.g.

a = l x l is the same as saying:
±a = x
ahh - i see! thanks!!!
0
Bhaal85
Badges: 9
Rep:
?
#7
Report 15 years ago
#7
(Original post by Silly Sally)
ahh - i see! thanks!!!
Though in the case of:

l a l = l x l you can't do it.
0
Lithium
Badges: 13
Rep:
?
#8
Report 15 years ago
#8
(Original post by Bhaal85)
Though in the case of:

l a l = l x l you can't do it.

WHY NOT?
0
RobbieC
Badges: 15
Rep:
?
#9
Report 15 years ago
#9
l 3x+5 l = l 5x l
Squaring both sides gives...

9x^2 + 30x +25 = 25x^2
Collecting like terms...

16x^2 - 30x -25.

Factorising...
(8x + 5) (2x - 5)

x = -5/8 or 5/2...

So why was everyone jabbering about an a??? That's the method I would use...Drawing graphs is too time consuming and often far less accurate...
0
X
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

If you do not get the A-level grades you want this summer, what is your likely next step?

Take autumn exams (21)
40.38%
Take exams next summer (12)
23.08%
Change uni choice through clearing (13)
25%
Apply to uni next year instead (5)
9.62%
I'm not applying to university (1)
1.92%

Watched Threads

View All
Latest
My Feed