a) 998.34=(1000−2).34=34000−68=33932

b,\(1990.1990-\left(1990+2\right).1988=1990.1990-1990.1988-2.1988=1990\left(1990-1988\right)-2.1988=1990.2-2.1998=2\left(1990-1998\right)=2.2\)= 4

c. \(\text{(1374.57+678.86).(26.13+74.14)}\)

Câu này đề hơi lạ

a) \(998.34=\left(1000-2\right).34=34000-68=33932\)

dễ quá lấy máy tính mà ấn

1990.1990-1992.1998=-19916

...............................=100

...............................=1

k mink nha

dễ thì làm đi Pháp Sư Áo Trắng

a) Xét 1992.1998 = (1995 - 3).(1995 + 3) = 1995.(1995 + 3) - 3.(1995 + 3) = 1995² + 1995.3 - 3.1995 - 3² = 1995² - 9

Vậy 1995² - 1992.1998 = 1995² - (1995² - 9) = 9

bang 9

Ngô thị dân tuyền chép của Phan Thanh Tịnh        mình sẽ ko k đâu

a, 4

b, 100

c, / ko biết là cái j nên ko giải đc

a, 1990 . 1990 - 1992 . 1988

=  3960100      - 3960096

= 4 .

b, ( 1374 . 57 + 687 . 86 ) : ( 26 . 13 + 74 . 14 )

=  ( 78318      + 59082    ) : ( 338       + 1036    )

=          137400                   :      1374

=                              100 .

c, \(\frac{37.13-13}{24 +37.12}\)

\(=\frac{37.\left(12+1\right)-13}{24+37.12}\)

\(=\frac{37.12+37-13}{24+37.12}\)

\(=\frac{37.12+24}{24+37.12}\)

\(=1\)

a. 19991999.1998 - 19981998.1999
=1999.10001.1998 - 1998.10001.1999
=0
b.(1374.57+687.86):(26.13+74.14)
=(687.2.57+687.86):(338+1036)
=\([687.\left(2.57+86\right)]:1374\)
=678.200:1374
=137400:1374
=100

 a) 
1990.1990 -1992.1998 = (1995-5)^2 -(1995+3)(1995-3) = -10.1995 +25 +9 = -(19950-34) = -19916 
b) 
ta có
tu = 124 .237 +152 = 122.137 + 474 +152= 122. 137 + 626 
mau = ( 870 + (237-2).122= 870 +122.237 - 244 =122.237 + 626 
=> phân thức đã cho = tử/mẫu = 1

a/ \(=1990.1990-\left(1990+2\right).\left(1990-2\right)=1990.1990-\left(1990.1990-4\right)=4\)

b/ \(=\frac{2.687.57+687.86}{26.13+74.\left(13+1\right)}=\frac{687\left(2.57+86\right)}{26.13+74.13+74}=\frac{687.\left(114+86\right)}{13\left(26+74\right)+74}=\)

\(=\frac{687.200}{13.100+74}=\frac{687.200}{1374}=\frac{687.200}{687.2}=\frac{200}{2}=100\)

c/ \(=\frac{214.237+152}{870+\left(237-2\right).\left(124-2\right)}=\frac{124.237+152}{870+124.237-2.237-2.124+4}=\)

\(=\frac{124.237+152}{124.237+870+4-2.237-2.124}=\frac{124.237+152}{124.237+152}=1\)

cảm ơn nha Nguyễn Ngọc Anh Minh!

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)