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Cảm ơn nhưng mình tìm ra đáp án rồi :
\(\frac{-1997\times1996+1}{\left(-1995\right)\left(-1997\right)+1996}=\frac{-1997\times\left(1995+1\right)+1}{1995\times1997+1996}=\frac{-1997\times1995-1997+1}{1995\times1997+1996}=\frac{-1997\times1995-1996}{1995\times1997+1996}=\frac{-\left(1997\times1995+1996\right)}{1995\times1997+1996}=-1\)
a: \(\dfrac{40.2\cdot8.1\cdot4.8}{0.048\cdot0.81}=40.2\cdot\dfrac{8.1}{0.81}\cdot\dfrac{4.8}{0.048}\)
\(=40.2\cdot10\cdot100=402\cdot100=40200\)
b: \(\dfrac{45\cdot16-17}{45\cdot15+28}=\dfrac{720-17}{675+28}=\dfrac{703}{703}=1\)
\(A=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{100}}\\ 2A=1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^{99}}\\ 2A-A=\left(1+\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^{99}}\right)-\left(\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{100}}\right)\\ A=1-\dfrac{1}{2^{100}}\)
\(E=\dfrac{3^2}{2\cdot4}+\dfrac{3^2}{4\cdot6}+...+\dfrac{3^2}{198\cdot200}\\ =3^2\cdot\left(\dfrac{1}{2\cdot4}+\dfrac{1}{4\cdot6}+...+\dfrac{1}{198\cdot200}\right)\\ =9\cdot\dfrac{1}{2}\cdot\left(\dfrac{2}{2\cdot4}+\dfrac{2}{4\cdot6}+...+\dfrac{2}{198\cdot200}\right)\\ =\dfrac{9}{2}\cdot\left(\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+...+\dfrac{1}{198}-\dfrac{1}{200}\right)\\ =\dfrac{9}{2}\cdot\left(\dfrac{1}{2}-\dfrac{1}{200}\right)\\ =\dfrac{9}{2}\cdot\dfrac{99}{200}\\ =\dfrac{891}{400}\)
a) \(A=125\left(-24\right)+24.225\)
\(=24\left[\left(-125\right)+225\right]\)
\(=24.100=2400\)
b) \(B=26\left(-125\right)-125\left(-36\right)\)
\(=125\left[\left(-26\right)-\left(-36\right)\right]\)
\(=125.10=1250\)
c) \(C=25\left(75-45\right)-75\left(45-25\right)\)
\(=25.75-25.45-75.45-75.25\)
\(=\left(25.75-75.25\right)-25.45-75.45\)
\(=-25.45-75.45\)
\(=45\left(-25-75\right)\)
\(=45\left(-100\right)=-4500\)
-5 + (-37 - 45 + 51) - (-37 + 51)
= -5 - 37 - 45 + 51 + 37 - 51
= - (5 + 45) - (37 - 37) + (51 - 51)
= - 50 - 0 + 0
= - 50
- (15 - 47 + 58) + (15 - 47 ) + 3
= - 15 + 47 - 58 + 15 - 47 + 3
= (-15 + 15) + (47 - 47) - (58 - 3)
= 0 + 0 - 55
= - 55
(53 - 45 - 49) - (53 + 45 - 49)
= 53 - 45 - 49 - 53 - 45 + 49
= (53 - 53) + (-49 + 49) - (45 + 45)
= 0 + 0 - 90
= - 90
13 - 15 + 49 - 13 + 15 - 48
= (13 - 13) + (-15 + 15) + (49 - 48)
= 0 + 0 + 1
= 1
\(=\left(45\cdot128-45\cdot128\right)\cdot\left(45\cdot46+47\cdot48\right)\cdot\left(51\cdot52-49\cdot48\right)\cdot\left(1995\cdot1996+1997\cdot1998\right)\)
=0*A
=0