kinu

07-12-2011, 06:45 AM

find Integer value of a for which the equation |2x+1|+|x-2|=a have only integer roots.

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kinu

07-12-2011, 06:45 AM

find Integer value of a for which the equation |2x+1|+|x-2|=a have only integer roots.

daon

07-12-2011, 08:07 AM

If I am interpreting this correctly, I would start with partitioning the real line by the zeros of the function stuck into the absolute values: -1/2 and 2

x <= -1/2

You get: -(2x+1)-(x-2)=a

-1/2 < x <= 2

You get: (2x+1)-(x-2)=a

x > 2

You get: (2x+1)+(x-2)=a

In the first case: -3x+1=a gives the only possible integer values a=1-3k for which x=k will be a root.

Try the others.

x <= -1/2

You get: -(2x+1)-(x-2)=a

-1/2 < x <= 2

You get: (2x+1)-(x-2)=a

x > 2

You get: (2x+1)+(x-2)=a

In the first case: -3x+1=a gives the only possible integer values a=1-3k for which x=k will be a root.

Try the others.

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