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c)c)
x-199+x-397+x-595<x-298+x-496+x-694x−199+x−397+x−595<x−298+x−496+x−694
⇔(x-199-1)+(x-397-1)+(x-595-1)<(x-298-1)+(x-496-1)+(x-694-1)⇔(x−199−1)+(x−397−1)+(x−595−1)<(x−298−1)+(x−496−1)+(x−694−1)
⇔x-10099+x-10097+x-10095-x-10098-x-10096-x-10094<0⇔x−10099+x−10097+x−10095−x−10098−x−10096−x−10094<0
⇔(x-100)(199+197+195-198-196-194)<0⇔(x−100)(199+197+195−198−196−194)<0
Vì 199+197+195-198-196-194<0199+197+195−198−196−194<0
⇒x-100>0⇒x−100>0
⇔x>100⇔x>100
Vậy S={x∣x>100}S={x∣x>100}.
d)d)
x-10091001+x-41003+x+20101005≤7x−10091001+x−41003+x+20101005≤7
⇔(x-10091001-1)+(x-41003-2)+(x+20101005-4)≤0⇔(x−10091001−1)+(x−41003−2)+(x+20101005−4)≤0
⇔x-20101001+x-20101003+x-20101005≤0⇔x−20101001+x−20101003+x−20101005≤0
⇔(x-2010)(11001+11003+11005)≤0⇔(x−2010)(11001+11003+11005)≤0
Vì 11001+11003+11005>011001+11003+11005>0
⇒x-2010≤0⇒x−2010≤0
⇔x≤2010⇔x≤2010
Vậy S={x∣x≤2010}S={x∣x≤2010}.
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