Đáp án:
Giải thích các bước giải:
Bài 1:
a)5.(−8).(−2).(−3)=[5.(−2)].[(−8).(−3)]=(−10).24=−240b)4.(−5)2+2.(−5)−20=4.(−5)2−10−20=4.25−30=100−30=70c)27.(15−12)−15.(27−12)=27.15−27.12−15.27+15.12=12(15−27)=12.12=144d)1−2+3−4+5−6+...+199−200=−1−1−1...−1=(−1).100=−100a)5.(−8).(−2).(−3)=[5.(−2)].[(−8).(−3)]=(−10).24=−240b)4.(−5)2+2.(−5)−20=4.(−5)2−10−20=4.25−30=100−30=70c)27.(15−12)−15.(27−12)=27.15−27.12−15.27+15.12=12(15−27)=12.12=144d)1−2+3−4+5−6+...+199−200=−1−1−1...−1=(−1).100=−100
(có 200 số mà 2 số nguyên liên tiếp có tổng bằng -1. suy ra số cặp như vậy là 200:2=100)
Bài 2:
a) 11+15−x=1⇔26−x=1⇔−x=1−26=−25⇔x=2511+15−x=1⇔26−x=1⇔−x=1−26=−25⇔x=25
b) b.2x−35=15⇔2x=15+35=50⇔x=25b.2x−35=15⇔2x=15+35=50⇔x=25
c)2|x+5|=12⇔|x+5|=6⇔x+5=6,x+5=−6⇔x=1,x=−112|x+5|=12⇔|x+5|=6⇔x+5=6,x+5=−6⇔x=1,x=−11
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