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\(A=\frac{10}{1\cdot2}+\frac{10}{2\cdot3}+\frac{10}{3\cdot4}+...+\frac{10}{98\cdot99}+\frac{10}{99\cdot100}\)
\(A=\frac{10}{1}-\frac{10}{2}+\frac{10}{2}-\frac{10}{3}+\frac{10}{3}-\frac{10}{4}+...+\frac{10}{99}-\frac{10}{100}\)
\(A=\frac{10}{1}-\frac{10}{100}\)
\(A=\frac{99}{10}\)
Không chắc nhá
\(A=\frac{10}{1\cdot2}+\frac{10}{2\cdot3}+\frac{10}{3\cdot4}+....+\frac{10}{98\cdot99}+\frac{10}{99\cdot100}\)
\(A=10\left(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{98\cdot99}+\frac{1}{99\cdot100}\right)\)
\(A=10\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{99}-\frac{1}{100}\right)\)
\(A=10\left(1-\frac{1}{100}\right)=10\cdot\frac{99}{100}=\frac{99}{10}\)
1+2+3+4+5+6+7+8+9+10
=(1+10)+(2+9)+(3+8)+(4+7)+(5+6)
=11+11+11+11+11
=11x5
=55
#)Giải :
\(\frac{1}{11}+\frac{2}{11}+\frac{3}{11}+\frac{4}{11}+\frac{5}{11}+\frac{6}{11}+\frac{7}{11}+\frac{8}{11}+\frac{9}{11}+\frac{10}{11}\)
\(=\left(\frac{1}{11}+\frac{10}{11}\right)+\left(\frac{2}{11}+\frac{9}{11}\right)+\left(\frac{3}{11}+\frac{8}{11}\right)+\left(\frac{4}{11}+\frac{7}{11}\right)+\left(\frac{5}{11}+\frac{6}{11}\right)\)
\(=1+1+1+1+1\)
\(=5\)
#~Will~be~Pens~#
\(\frac{6}{7}..........\frac{8}{10}\)
\(\Rightarrow\frac{6}{7}=\frac{60}{70}\);\(\frac{8}{10}=\frac{56}{70}\)
\(\frac{60}{70}>\frac{56}{70}\) Nên \(\frac{6}{7}>\frac{8}{10}\)
A = 10/1x2 + 10/2x3 + 10/3x4 +........ + 10/98x99 + 10/99x100
A=10x(1/1x2+1/2x3+1/3x4+..+1/98x99+1/99x100)
A= 10x( 1-1/2+1/2-1/3+1/3-1/4+..+1/99-1/100)
A=10x( 1-1/100)
A=10x99/100
A=99/10
A = đề
A=10x(1/1x2+1/2x3+1/3x4+..+1/98x99+1/99x100)
A= 10x( 1-1/2+1/2-1/3+1/3-1/4+..+1/99-1/100)
A=10x( 1-1/100)
A=10x99/100
A=99/10
\(\frac{1}{5}\div\frac{8}{10}\)
\(=\frac{1}{5}\times\frac{10}{8}\)
\(=\frac{10}{40}\)
\(=\frac{1}{4}\)
\(\frac{1}{5}:\frac{8}{10}=\frac{1}{5}.\frac{10}{8}=\frac{1}{5}.\frac{5}{4}=\frac{1.1}{1.4}=\frac{1}{4}\)