Tính nhanh :
A, 1997 + 24 =
B, 29 + 1994
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1996 x 1997 + 1998 x 3 + 1994 / 1997 x 1999 - 1997 x 1997
= 1996 x 1997 + ( 1997 + 1 x 3 ) + 1994 / 1997 x 1999 - 1997 x 1997
= 1996 x 1998 + 1 x 3 + 1994 / 1997 x 1999 - 1997 x 1997
= 3988008 + 3 + 1994 / 1997 x 1999 - 1997 x 1997
= 3990005 / 1997 x 1999 - 1997 x 1997
= 3990005 / ( 1999 - 1997 ) x 1997
= 3990005 / 3994
\(B=\)\(\frac{3+33+333+3333+33333}{4+44+444+4444+44444}\)
\(B=\frac{3.1+3.11+3.111+3.1111+3.11111}{4.1+4.11+4.111+4.1111+4.11111}\)
\(B=\frac{3.\left(1+11+111+1111+11111\right)}{4.\left(1+11+111+1111+11111\right)}\)
\(B=\frac{3}{4}\)
\(A=\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}+\frac{1}{192}\)
\(A.2=\left(\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}+\frac{1}{192}\right).2\)
\(A.2=\frac{2}{3}+\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}\)
=>\(A.2-A=\left(\frac{2}{3}+\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}\right)-\left(\frac{1}{3}+\frac{1}{6}+\frac{1}{12}+\frac{1}{24}+\frac{1}{48}+\frac{1}{96}+\frac{1}{192}\right)\)
\(A=\frac{2}{3}-\frac{1}{192}\)
\(A=\frac{127}{192}\)
\(\frac{1995}{1997}.\frac{1990}{1993}.\frac{1997}{1994}.\frac{1993}{1995}.\frac{997}{995}\)
Đặt \(C=\frac{1995}{1997}.\frac{1990}{1993}.\frac{1997}{1994}.\frac{1993}{1995}.\frac{997}{995}\)
\(C=\frac{1995.1990.1997.1993.997}{1997.1993.1994.1995.995}\)
\(C=\frac{1990.997}{1994.995}\)
\(C=\frac{995.2+997}{997.2+995}=1\)
\(B=\frac{3+33+333+3333+ 33333}{4+44+444+4444+44444}\)
\(\Rightarrow B=\frac{3\left(1+11+111+1111+11111\right)}{4\left(1+11+111+1111+11111\right)}=\frac{3}{4}\)
1995*1997-1/1996*1995+1994
=1995*(1996+1)-1/1996*1995+1994
=1995*1996+1995-1/1996*1995+1994
=1995*1996+1994/1996*1995+1994
=1
ủng hộ mk nha!!
Bạn Nguyen Thi Nhung à! Câu trả lời của mình cũng giống như của bạn Hanyou Inu thôi.
(1-2-3+4)+(5-6-7+8)+.....+(1993-1994-1995+1996)+1997
=0+0+....+0+1997
=1997
a2021
b2023
A. 1997 + 24 = (1997 + 3) + (24 - 3)
= 2000 + 21
= 2021
B. 29 + 1994 = (29 - 6) + (1994 + 6)
= 23 + 2000
= 2023