Thu gọn biểu thức sau : \(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+...+\frac{2}{2004.2005}\)
tính:\(M=\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+...+\frac{2}{2004.2005}\)
\(M=\frac{1}{2}+\frac{1}{6}+\frac{1}{10}+....+\frac{2}{2004.2005}\)
\(\Leftrightarrow2M=\frac{2}{2.3}+\frac{2}{3.4}+\frac{2}{4.5}+.....+\frac{2}{2004.2005}\)
\(=2.\left(\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+....+\frac{1}{2004.2005}\right)\)
\(=2.\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+....+\frac{1}{2004}-\frac{1}{2005}\right)\)
\(=2.\left(\frac{1}{2}-\frac{1}{2005}\right)\)
\(=2.\left(\frac{2005}{4010}-\frac{2}{4010}\right)\)
\(=2.\frac{2003}{4010}\)
\(=\frac{2003}{2005}\)
\(M=\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+...+\frac{2}{2004\cdot2005}\)
\(M=\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+\frac{2}{30}+...+\frac{2}{2004\cdot2005}\)
\(M=2\left(\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{2004\cdot2005}\right)\)
\(M=2\left(\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+...+\frac{1}{2004\cdot2005}\right)\)
\(M=2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{2004}-\frac{1}{2005}\right)\)
\(M=2\left(\frac{1}{2}-\frac{1}{2005}\right)\)
\(M=2\cdot\frac{2003}{4010}\)
\(M=\frac{2003}{2005}\)
dễ mà:
Chú ý vào số cuối cùng nhé bạn nó là dấu hiệu để làm đó
M=2/6+2/12+2/20+.....+2/2004x2005
M=2(1/2x3+1/3x4+.....+1/2004x2005)
M=2(1/2-1/3+1/3-1/4+.....+1/2004-1/2005)
M=2(1-1/2005)
M=2(2004/2005)
M=4008/2005
thu gọn biểu thức sau
\(A=\left(\frac{15}{\sqrt{6}+1}+\frac{4}{\sqrt{6}-2}-\frac{12}{3-\sqrt{6}}\right).\left(\sqrt{6}+11\right)\)
Thu gọn biểu thức sau : \(A=\frac{1}{10}-\frac{1}{20}-\frac{1}{30}-\frac{1}{42}-\frac{1}{56}-\frac{1}{72}-\frac{1}{90}\)
\(A=\frac{1}{10}-\left(\frac{1}{20}+\frac{1}{30}+....+\frac{1}{90}\right)=\frac{1}{10}-\left(\frac{1}{4.5}+\frac{1}{5.6}+.....+\frac{1}{9.10}\right)\)
\(=\frac{1}{10}-\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...-\frac{1}{10}\right)=\frac{1}{10}-\left(\frac{1}{4}-\frac{1}{10}\right)=\frac{1}{5}-\frac{1}{4}=\frac{-1}{20}\)
\(A=\frac{1}{10}-\frac{1}{20}-\frac{1}{30}-\frac{1}{42}-\frac{1}{56}-\frac{1}{72}-\frac{1}{90}\)
\(A=\frac{1}{10}-\left(\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+...+\frac{1}{90}\right)\)
\(A=\frac{1}{10}-\left(\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{9.10}\right)\)
\(A=\frac{1}{10}-\left(\frac{1}{4}-\frac{1}{5}+...+\frac{1}{9}-\frac{1}{10}\right)\)
\(A=\frac{1}{10}-\left[\left(\frac{1}{4}-\frac{1}{10}\right)-\left(\frac{1}{5}-\frac{1}{5}\right)-...-\left(\frac{1}{9}-\frac{1}{9}\right)\right]\)
\(A=\frac{1}{10}-\frac{1}{4}+\frac{1}{10}\)
\(A=\frac{1}{5}-\frac{1}{4}\)
\(A=-\frac{1}{20}\)
Tính giá trị của biểu thức:
\(\frac{\left(\frac{1}{6}+\frac{1}{10}+\frac{1}{15}\right):\left(\frac{1}{6}+\frac{1}{10}-\frac{1}{15}\right)}{\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{4}-\frac{1}{5}\right):\left(\frac{1}{4}-\frac{1}{6}\right)}\)
Rút gọn các biểu thức sau:\(\frac{\frac{1}{2}-\frac{1}{3}+\frac{2}{5}+\frac{1}{8}}{\frac{1}{6}+\frac{3}{20}-\frac{1}{3}+\frac{3}{4}}\)
THU GỌN BIỂU THỨC SAU
\(\left(\frac{n-1}{1}+\frac{n-2}{2}+\frac{n-3}{3}+...+\frac{2}{n-2}+\frac{1}{n-1}\right):\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{n}\right)\)
Thu gọn biểu thức sau:
\(N=\frac{1}{2}-\frac{1}{^{2^2}}+\frac{1}{2^3}-\frac{1}{2^4}+...+\frac{1}{2^{49}}-\frac{1}{2^{50}}\)
Rút gọn các biểu thức sau \(\left( {a > 0,b > 0} \right)\):
a) \({a^{\frac{1}{3}}}{a^{\frac{1}{2}}}{a^{\frac{7}{6}}}\);
b) \({a^{\frac{2}{3}}}{a^{\frac{1}{4}}}:{a^{\frac{1}{6}}}\);
c) \(\left( {\frac{3}{2}{a^{ - \frac{3}{2}}}{b^{ - \frac{1}{2}}}} \right)\left( { - \frac{1}{3}{a^{\frac{1}{2}}}{b^{\frac{3}{2}}}} \right)\).
a) \(a^{\dfrac{1}{3}}\cdot a^{\dfrac{1}{2}}\cdot a^{\dfrac{7}{6}}=a^{\dfrac{1}{3}+\dfrac{1}{2}+\dfrac{7}{6}}=a^2\)
b) \(a^{\dfrac{2}{3}}\cdot a^{\dfrac{1}{4}}:a^{\dfrac{1}{6}}=a^{\dfrac{2}{3}+\dfrac{1}{4}-\dfrac{1}{6}}=a^{\dfrac{3}{4}}\)
c) \(\left(\dfrac{3}{2}a^{-\dfrac{3}{2}}\cdot b^{-\dfrac{1}{2}}\right)\left(-\dfrac{1}{3}a^{\dfrac{1}{2}}b^{\dfrac{2}{3}}\right)=\left(\dfrac{3}{2}\cdot-\dfrac{1}{3}\right)\left(a^{-\dfrac{3}{2}}\cdot a^{\dfrac{1}{2}}\right)\left(b^{-\dfrac{1}{2}}\cdot b^{\dfrac{2}{3}}\right)\)
\(=-\dfrac{1}{2}a^{-1}b^{-\dfrac{1}{3}}\)
THU GỌN BIỂU THỨC SAU
\(\left(\frac{n-1}{1}+\frac{n-2}{2}+\frac{n-3}{3}+...+\frac{2}{n-2}+\frac{1}{n-1}\right):\left(\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{n}\right)\)