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= 1/3 - 1/3 + 5/7 - 5/7 - 7/9 + 7/9 +9/11 - 9/11 -11/13 + 11/13 +13/15
= 0 + 0 - 0 + 0 -0 + 13/15
= 0 + 13/15
= 13/15
\(\frac{1}{3}-\frac{3}{5}+\frac{5}{7}-\frac{7}{9}+\frac{9}{11}-\frac{11}{13}+\frac{13}{15}+\frac{11}{13}-\frac{9}{11}+\frac{7}{9}-\frac{5}{7}+\frac{3}{5}-\frac{1}{3}\)
\(=\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{3}{5}-\frac{3}{5}\right)+\left(\frac{5}{7}-\frac{5}{7}\right)+\left(\frac{7}{9}-\frac{7}{9}\right)+\left(\frac{9}{11}-\frac{9}{11}\right)+\left(\frac{11}{13}-\frac{11}{13}\right)+\frac{13}{15}\)
\(=0+0+0+0+0+0+\frac{13}{15}\)
\(=\frac{13}{15}\)
a=(1/3-1/3)+(3/5-3/5)+(5/7-5/7)+(9/11-9/11)+(11/13-11/13)+13/15
a=13/15
A= 1/3- 3/4+ 3/5+ 1/72- 2/9- 1/36+ 1/15
A= ( 1/3- 3/5+ 1/15) - (3/4- 1/72+ 2/9+ 1/36)
A= (5/15- 9/15+ 1/15) - (54/72- 1/72+ 16/72+ 2/36)
A= 1- 71/72
A= 1/72
=3/4-3/5+3/7+3/13 / 11/4-11/5+11/7+11/13 + 3/4-3/5+3/7+3/13 / 11/4-11/5+11/7+11/13
=3.1/4-3.1/5+3.1/7+3.1/13 / 11.1/4-11.1/5+11.1/7+11.1/13 + 3.1/4-3.1/5+3.1/7+3.1/13 / 11. 1/4-11.1/5+11.1/7+11.1/13
=3.(1/4-1/5+1/7+1/13) / 11.(1/4-1/5+1/7+1/13) + 3.(1/4-1/5+1/7+1/13) / 11.(1/4-1/5+1/7+1/13)
=3/11+3/11
=6/11
Ta có:\(P=\frac{\frac{3}{4}-\frac{3}{5}+\frac{3}{7}+\frac{3}{13}}{\frac{11}{3}-\frac{11}{5}-\frac{11}{7}-\frac{11}{13}}\)
\(\Rightarrow P=\frac{3.\left(\frac{1}{4}-\frac{1}{5}+\frac{1}{7}+\frac{1}{13}\right)}{11.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{7}+\frac{1}{13}\right)}\)
\(\Rightarrow P=\frac{3}{11}\)
Chắc bạn gõ nhầm số hạng thứ 3 phải là +5/7.
Tổng này đối xứng qua 13/15. Các đối xứng trái dấu nên Tổng = 13/15
a) \(\frac{1}{3}-\frac{3}{5}+\frac{5}{7}-\frac{7}{9}+\frac{9}{11}-\frac{11}{13}+\frac{13}{5}+\frac{11}{13}-\frac{9}{11}+\frac{7}{9}-\frac{5}{7}+\frac{3}{5}-\frac{1}{3}\)
=\(\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{5}{7}-\frac{5}{7}\right)+\left(\frac{7}{9}-\frac{7}{9}\right)+\left(\frac{11}{13}-\frac{11}{13}\right)+\frac{13}{5}\)
=\(\frac{0}{3}+\frac{0}{7}+\frac{0}{9}+\frac{0}{13}+\frac{13}{15}\)
=\(0+0+0+0+\frac{13}{5}\)
=\(\frac{13}{5}\)
\(\frac{1}{3}-\frac{3}{5}+\frac{5}{7}-\frac{7}{9}+\frac{9}{11}-\frac{11}{13}+\frac{13}{5}+\frac{11}{13}-\frac{9}{11}+\frac{7}{9}-\frac{5}{7}+\frac{3}{5}-\frac{1}{3}\)
\(=\left(\frac{1}{3}-\frac{1}{3}\right)+\left(\frac{-3}{5}+\frac{3}{5}\right)+\left(\frac{5}{7}-\frac{5}{7}\right)+\left(\frac{-7}{9}+\frac{7}{9}\right)+\left(\frac{-11}{13}+\frac{11}{13}\right)+\frac{13}{5}\)
\(=0+0+0+0+0+\frac{13}{5}\)
\(=\frac{13}{5}\)
Chúc bạn học tốt !
[3.(1/4-1/5+1/7+1/11)] / [13.(1/4-1/5+1/7+1/11)]
=3/13
tk tui nha
\(\frac{\frac{3}{3}-\frac{3}{5}+\frac{3}{11}+\frac{3}{13}}{\frac{7}{3}-\frac{7}{5}+\frac{7}{11}+\frac{7}{13}}=\frac{3x\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{11}+\frac{1}{13}\right)}{7x\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{11}+\frac{1}{13}\right)}=\frac{3}{7}\)\(\frac{3}{7}\)
5 mà bạn