Tìm x
(5^2/14 +5^2/84 +5^2/204 +5^2/374):5/8 -{45:[x+1,75):0,5
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\(1-\dfrac{5}{14}-\dfrac{5}{84}-\dfrac{5}{204}-\dfrac{5}{374}\) =\(1-\left(\dfrac{1}{1.14}+\dfrac{1}{14.6}+\dfrac{1}{6.34}+\dfrac{1}{34.11}\right)\)
= \(1-\left(\dfrac{1}{1}-\dfrac{1}{14}+\dfrac{1}{14}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{34}+\dfrac{1}{34}-\dfrac{1}{11}\right)\)
= 1 - \(\left(1-\dfrac{1}{11}\right)\) = \(1-\dfrac{10}{11}=\dfrac{1}{11}\)
\(=1-\dfrac{5}{2\cdot7}-\dfrac{5}{7\cdot12}-\dfrac{5}{12\cdot17}-\dfrac{5}{17\cdot22}\)
\(=1-\left(\dfrac{1}{2}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{12}+\dfrac{1}{12}-\dfrac{1}{17}+\dfrac{1}{17}-\dfrac{1}{22}\right)\)
\(=5-\dfrac{11-1}{22}=5-\dfrac{10}{22}=5-\dfrac{5}{11}=\dfrac{50}{11}\)
b. \(\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-....+\frac{1}{2003}\)= \(\frac{1}{2013}\)
c. \(5.\left(\frac{1}{14}+\frac{1}{84}+\frac{1}{204}+\frac{1}{374}\right)\)= 5. \(\frac{1}{11}\)= \(\frac{5}{11}\)
Mình biết 2 câu này thôi, thông cảm nhá...!!!
d) Ta có: 100-(1+1/2+1/3+1/4+...+1/100)
=1x100-(1+1/2+1/3+1/4+...+1/100)
=(1-1)+(1-1/2)+(1-1/3)+(1-1/4)+....+(1-1/100)
=1/2+2/3+3/4+...+99/100