Tính nhanh:
\(\frac{8018}{2004.2006-2003.2005}\)
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2004.2006-2003.2005
= ( 2004 - 2003 ) x ( 2006 - 2005 )
= 1 x 1
=1
\(\dfrac{8018}{2004.2006-2003.2005}\)
\(=\dfrac{8018}{\left(2005-1\right)\left(2005+1\right)-\left(2004-1\right)\left(2004+1\right)}\)
\(=\dfrac{8018}{2005^2-1^2-2004^2+1^2}=\dfrac{8018}{\left(2005-2004\right)\left(2005+2004\right)}\)
\(=\dfrac{8018}{1.4009}=2\)
Chúc bạn học tốt!!!
Đặt:
\(HANG=\dfrac{8018}{2004.2006-2003.2005}\)
\(HANG=\dfrac{8018}{\left(2005-1\right)\left(2005+1\right)-\left(2004-1\right)\left(2004+1\right)}\)
\(HANG=\dfrac{8018}{2005^2-1-2004^2+1}\)
\(HANG=\dfrac{8018}{2005^2-2004^2}\)
\(HANG=\dfrac{8018}{\left(2005-2004\right)\left(2005+2004\right)}\)
\(HANG=\dfrac{8018}{4009}=2\)
Vậy \(HANG=2\)
\(\frac{2004.2006+1000}{2005.2006-1006}\)
\(=\frac{2004.2006+1000}{\left(2004+1\right).2006-1006}\)
\(=\frac{2004.2006+1000}{2004.2006+2006-1006}\)
\(=\frac{2004.2006+1000}{2004.2006+1000}\)
\(=1\)
\(\frac{2004x2006+1000}{2005x2006-1006}\)
=\(\frac{1000}{1x2006-1006}\)cùng giảm 2004 lần số 2006
=\(\frac{1000}{1000}=1\)
A = \(\dfrac{5.4^{15}.9^9-4.3^{20}.8^9}{5.2^9.6^{19}-7.2^{29}.27^6}=\dfrac{5.2^{30}.3^{18}-2^{29}.3^{20}}{5.2^{28}.3.3^{19}-7.2^{29}.3^{18}}=\dfrac{2^{29}.3^{18}\left(5.2-3^2\right)}{2^{18}.3^{18}\left(5.3-7.2\right)}=2\)
B = \(\dfrac{8020}{2004.2006-2003.2005}\)
Đặt x = 2004, ta có:
\(\dfrac{4x+2}{x\left(x+2\right)-\left(x-1\right)\left(x+1\right)}=\dfrac{4x+2}{2x+1}=\dfrac{2\left(2x+1\right)}{2x+1}=2\)
Ta có:
A = \(\frac{2}{1.3}\)+ \(\frac{2}{3.5}\)+ \(\frac{2}{5.7}\)+ \(\frac{2}{7.9}\) + ... + \(\frac{2}{2001.2003}\) + \(\frac{2}{2003.2005}\)
= \(\frac{1}{1}\) - \(\frac{1}{3}\)+ \(\frac{1}{3}\)- \(\frac{1}{5}\)+ \(\frac{1}{5}\)- \(\frac{1}{7}\)+ \(\frac{1}{7}\)- \(\frac{1}{9}\) + ... + \(\frac{1}{2001}\)- \(\frac{1}{2003}\)+ \(\frac{1}{2003}\)- \(\frac{1}{2005}\)
= 1 - \(\frac{1}{2005}\)
= \(\frac{2004}{2005}\)
Chúc bạn học tốt nha ^^!!
\(A=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{2003.2005}\)
\(2A=2.\left(\frac{1}{1.3}+\frac{1}{2.5}+\frac{1}{5.7}+...+\frac{1}{2003.2005}\right)\)
\(2A=\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{2003.2005}\)
\(2A=1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2003}-\frac{1}{2005}\)
\(2A=1-\frac{1}{2005}\)
\(2A=\frac{2004}{2005}\)
\(A=\frac{2004}{2005}:2\)
\(A=\frac{1002}{2005}\)
Ủng hộ tk Đúng nha mọi người !!! ^^
Đặt B = \(\frac{1}{1.3}\)+ \(\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{2003.2005}\Rightarrow2B=2\left(\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{2003.2005}\right)\)\(\Rightarrow2B=\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+...+\frac{2}{2003.2005}\Rightarrow2B=\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{2003}-\frac{1}{2005}\)
\(\Rightarrow2B=\frac{1}{3}-\frac{1}{2005}=\frac{2012}{6015}\Rightarrow B=\frac{2012}{6015}:2=\frac{1001}{6015}\)
Cho tổng trên là A
\(A=\frac{1}{1.3}+\frac{1}{3.5}+\frac{1}{5.7}+...+\frac{1}{2003.2005}\)
\(A=2\left(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{2003}-\frac{1}{2005}\right)\)
\(A=2\left(1-\frac{1}{2005}\right)\)
\(A=2.\frac{2004}{2005}\)
\(A=\frac{4008}{2005}\)
\(\dfrac{8018}{2004.2006-2003.2005}\)
=\(\dfrac{8018}{\left(2005-1\right).\left(2005+1\right)-\left(2004-1\right).\left(2004+1\right)}\)
=\(\dfrac{8018}{2005^2.1^2-2004^2+1^2}\)
=\(\dfrac{8018}{\left(2005-2004\right).\left(2005.2004\right)}\)
=\(\dfrac{8018}{1.4009}\)
= 2
nó = 2 nhé
gợi ý
cái mẫu dùng hăng đẳng thức phá hết ra, rồi tòi ra mẫu = 4009