## The problem

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I do not understand the solution being all numbers

## Answer provided by our tutors

By definition the absolute value of any number is a non-negative number.

So, one side you have absolute value |1 - 4k| and on the other a negative number -11.

|1 - 4k|>=0 for all numbers k,

and 0 > -11 thus for all number k the following is true: