+0  
 
0
708
4
avatar

solve x2 - 3|x| + 4 = 0

 Jan 6, 2017
 #1
avatar+259 
0

Lets say x is positive:

 

2x-3x+4=0

 

-1x+4=0.  I-4

 

-1x=-4

 

x=4

 

Now lets say x is negative:

(Im not sure about the answer)

 

First i try to isolate the absolute value x:

 

2x-3IxI+4=0.     I-2x

 

-3IxI+4=-2x.      I -4

 

-3IxI=-2x-4.       I/-3

 

IxI.  =. 2/3x. + 4/3x

 

So x = 2/3x+ 4/3x if x is positive, which gives u 4 if u plot it back into the equation or:

 

x=-(2/3x + 4/3x)

 

x= -2/3x -4/3x

 

if x is negativ.   

 

At this step im not really sure, so it can be false but if you plot this now back into the equation for IxI u get:

 

2x-3*(-2/3x - 4/3x)+4=0

 

Solve it and u get x=-0.5

 

So you got 2 answers of L{4, -0.5}

 

Both seem to work, but i guess theres a much easier way to get the result.

 Jan 6, 2017
edited by amnesia  Jan 6, 2017
edited by amnesia  Jan 6, 2017
edited by amnesia  Jan 6, 2017
 #3
avatar+259 
+5

Well I made a mistake in the calcuation above. Everything starting from the part where I assume IxI is negative is wrong.

 

IxI.  =. 2/3x. + 4/3

This is correct if x=8 or x= -0.8

 

IxI.  = 2/3x + 4/3 is true when

x = 2/3x+4/3 or x = -2/3x -4/3

 

Dont know how to calculate those though. 

amnesia  Jan 6, 2017
 #4
avatar+259 
0

Oh wow... Im bad. Ment x= 4 or x= - 0.8 ...

im just going to sleep cant think straight anymore

amnesia  Jan 6, 2017
 #2
avatar+129852 
0

x^2 - 3|x| + 4 = 0

 

I don't  believe this has any "real" solutions......

 

See here :  https://www.desmos.com/calculator/pvwvwzobj7

 

 

 

cool cool cool

 Jan 6, 2017

3 Online Users

avatar