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yamatecuraxai

a) 1990.1990 - 1992.1988

= 1990.1990 - (1990 + 2)(1990 - 2)

= 1990.1990 - 1990.1990 + 4 = 4

b) (1374.57 + 687.86) : (870 + 235.122)

= (1374.57 + 687.2.43) : (10.87 + 5.47.2.61)

= (1374.57 + 1374.43) : (10.87 + 10.47.61)

= [1374(57 + 43)] : [10(87 + 47.61)]

= (1374.100) : [10(87 + 47.61)] (đoạn này mẫu số xấu quá, hetcuu)

c) (124.237 + 152) : (870 + 235.122)

= (124.235 + 124.2 + 152) : (870 + 235.122)

= (122.235 + 2.235 + 2.124 + 152) : (870 + 235.122)

= (122.235 + 470 + 248 + 152) : (235.122 + 870)

= (122.235 + 870) : (235.122 + 870) = 1

d) \(\dfrac{423134\cdot846267-423133}{846267\cdot423133+423134}=\dfrac{423133\cdot846267+846267-423133}{846267\cdot423133+423134}\)

\(=\dfrac{423133\cdot846267+423134}{846267\cdot423133+423134}=1\)

a)1990*1990-1992*1988=1990*(1988+2)-(1990+2)*1988=1990*1988+2*1990-1990*1988-2*1988=(1990*1988-1990*1988)+(2*1990-2*1988)=0+2*(1990-1988)=2*2=4

b)(1374*57+687*86)/(26*13+74*14)=(687*2*57+687*86)/(26*13+74+74*13)=(687*114+687*86)/(100*13+74)

=(687*200)/1374=137400/1374=100

c)(124*237+152)/(870+235*122)=\(\frac{\left(122+2\right)\cdot237+152}{870+\left(237-2\right)\cdot122}=\frac{122\cdot237+2\cdot237+152}{870-2\cdot122+237\cdot122}=\frac{122\cdot237+626}{626+237\cdot122}=1\)

d)\(\frac{423134\cdot846267-423133}{846267\cdot423133+423134}=\frac{\left(423133+1\right)\cdot846267-423133}{846267\cdot423133+423134}\)

\(=\frac{423133\cdot846267+846267-423133}{846267\cdot423133+423134}=\frac{423133\cdot846267+423134}{846267\cdot423133+423134}=1\)

(mỏi hết cả mắt)

bài này dễ mà 

mik đăng cho vui thôi

a)1990.1990+1992.1988

=3960100+3960096

=7920196

b)(124.237+152):(870+235.122)

=(29388+152):(870+28670)

=29540:29540

=1

c)(423134.846267-423133):(846267.423133+423134)

=(423134.846267):(423133-423134)

=(423134.846267):0

=0