Thursday, 14 March 2013

algebra precalculus - Solve an absolute value equation simultaneously



My question is :




Solve simultaneously
{|x1||y2|=1y=3|x1|





What I did :
y=3|x1| is given.



Thus y=3(x1) or y=3((x1)), and so y=4x or y=2+x.



If y=2+x, then x1=4y(1) or y2=x(2).



Substituting 1), we get |4y||y2|=1 or |y21||y2|=1.




I got here but I am not getting how to get the final solution. Any help would be greatly appreciated.


Answer



You have that |x1||y2|=1. This gives us that |x1|=1+|y2|.

Plugging this into the second equation gives us y=3(1+|y2|)=2|y2|

This gives us that y+|y2|=2.

If y2, then we get that y+y2=2y=2

If y<2, then we get that y+2y=2
which is true for all y<2. Hence we get that y2
From the second equation, we get that |x1|=3y

Note that since y2, 3y>0 always.



If x>1, then x1=3yx=4y

Note that 4y>1, since y2.




If x1, then x1=y3x=y2

Note that y21, since y2.



Hence, the solution set is given as follows. y2 and x=4y or y2


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