Question

help with calc

Answer 1

|f(x)|=f(x) if f(x)>0
|f(x)|=-f(x) if f(x)<0
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|x-4|=x-4 if x-4>0 (x>4)
|x-4|=-(x-4) if x-4<0 (x<4)
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so if we are looking to the left of 4 then we are looking at values smaller than 4
so |x-4|=-(x-4) in your case