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\(B=\dfrac{1}{3}+\dfrac{1}{15}+\dfrac{1}{35}+...+\dfrac{1}{97\times99}\)
\(=\dfrac{1}{1.3}+\dfrac{1}{3.5}+\dfrac{1}{5.7}+...+\dfrac{1}{97.99}\)
\(=\dfrac{1}{2}.\left(\dfrac{2}{1.3}+\dfrac{2}{3.5}+\dfrac{2}{5.7}+...+\dfrac{2}{97.99}\right)\)
\(=\dfrac{1}{2}.\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{97}-\dfrac{1}{99}\right)\)
\(=\dfrac{1}{2}.\left(1-\dfrac{1}{99}\right)\)
\(=\dfrac{1}{2}.\dfrac{98}{99}\)
\(=\dfrac{49}{99}\)
dấu \(.\) là dấu \(\times\)
1 + 4 : 2 x 6 - 2 + 5 x 3 - 8
= 1 + 2 x6 - 2 + 15 - 8
= 1 + 12 - 2 + 15 - 8
= 1 + 10 + 7
= 18
1 + 4 : 2 x 6 - 2 + 5 x 3 - 8
= 1 + 2 x 6 - 2 + 15 - 8
= 1 + 12 - 2 + 15 - 8
= 13 - 2 + 15 - 8
= 11 +15 - 8
= 26 - 8
= 18
1/4 + 1/3 : (2x - 1) = -5
=> 1/3 : (2x - 1) = -21/4
=> 2x - 1 = -63/4
=> 2x = -59/4
=> x = -59/8
\(\frac{1}{4}+\frac{1}{3}:\left(2x-1\right)=-5\)
\(\frac{1}{3}:\left(2x-1\right)=\left(-5\right)-\frac{1}{4}\)
\(\frac{1}{3}:\left(2x-1\right)=\frac{-21}{4}\)
\(2x-1=\frac{1}{3}:\frac{-21}{4}\)
\(2x-1=\frac{-4}{63}\)
\(2x=\frac{-4}{63}+1\)
\(2x=\frac{59}{63}\)
\(x=\frac{59}{63}:2\)
\(x=\frac{59}{126}\)
\(\frac{\frac{1}{3}+\frac{1}{9}-\frac{1}{27}}{\frac{5}{3}+\frac{5}{9}-\frac{5}{27}}=\frac{\frac{9}{27}+\frac{3}{27}-\frac{1}{27}}{\frac{45}{27}+\frac{15}{27}-\frac{5}{27}}=\frac{\frac{9+3-1}{27}}{\frac{45+15-5}{27}}=\frac{\frac{11}{27}}{\frac{55}{27}}=\frac{11}{55}=\frac{1}{5}.\)
1 + 1 = 2 nha bạn
1 + 1 = 2 nhé