Đáp án:
B7:
a)-214
b)-28
c)0
d)-1561
B8:
a)9
b)145
B9:
a)x=-5
b)x=4
c)x=-21
d)x=-1
Giải thích các bước giải:
B7:
a)(3567-214)-3567
=3567-214-3567
=-214
b)(-2017)-(28-2017)
=(-2017)-28+2017
=-28
c)-(269-357)+(269-357)
=-269+357+269-257
=0
d)(123+345)+(456-123)-[2017-(-345)]
=123+345+456-123-(2017+345)
=123+345+456-123-2017-345
=456-2017
=-1561
B8:
a)(17-229)+(17-25+229)
=17-229+17-25+229
=9
b)(125-679+145)-(125-679)
=125-679+145-125+679
=145
B9:
a)15-(4-x)=6
<=>15-4+x=6
<=>x=6-15+4
<=>x=-5
b)-30+(25-x)=-1
<=>-30+25-x=-1
<=>x=-1+30-25
<=>x=4
c)x-(12-25)=-8
<=>x-12+25=-8
<=>x=-8+12-25
<=>x=-21
d)(x-29)-(17-38)=-9
<=>x-29-17+38=-9
<=>x=-9+29+17-38
<=>x=-1
Học tốt!!!