Economist wrote:

when x<0, |x| = -x...so the first eq becomes

Y = -x + (-x) = -2x ?????

When x is negative, you don't replace x with -x; if x is negative, then -x is a positive number. If x is negative, there is a negative sign 'inside' of x.

Now, if x is negative, you

can replace |x| with -x, because if x is negative, -x will produce the 'positive equivalent' of x.

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