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(1 - 1/7) x (1 - 2/7) x ............(1 - 10/7)
= 6/7 x 5/7 x ..... x -3/7
=6/7 x 5/7x 4/7 x 3/7x 2/7 x 1/7 x 0 x -1/7x -2/7 x -3/7
=0
nhớ tk cho mình nha
Bài 1:
a, \(\frac{1}{-16}-\frac{3}{45}=\frac{-1}{16}-\frac{1}{15}\)
\(=\frac{-15}{240}-\frac{16}{240}\)
\(=\frac{-31}{240}\)
b, \(=\frac{-10}{12}-\frac{-12}{12}\)
\(=\frac{2}{12}=\frac{1}{6}\)
c, \(=\frac{-30}{6}-\frac{1}{6}\)
\(=\frac{-31}{6}\)
Bài 2:
a, \(x=-\frac{1}{2}-\frac{3}{4}\)
\(x=-\frac{1}{4}\)
b, \(\frac{1}{2}+x=-\frac{11}{2}\)
\(x=-\frac{11}{2}-\frac{1}{2}\)
\(x=-6\)
Bạn nhớ k đúng và chọn câu trả lời này nhé!!!! Mình giải đúng và chính xác hết ^_^
b) Áp dụng tính chất
\(\frac{a}{b}< 1\Rightarrow\frac{a}{b}< \frac{a+m}{b+m}\left(m\in N\right)\)
Ta có: \(B=\frac{10^{16}+1}{10^{17}+1}< \frac{10^{16}+1+9}{10^{17}+1+9}=\frac{10^{16}+10}{10^{17}+10}=\frac{10.\left(10^{15}+1\right)}{10.\left(10^{16}+1\right)}=\frac{10^{15}+1}{10^{16}+1}=A\)
\(\Rightarrow B< A\)
\(B< 1\Rightarrow\frac{10^{16}+1}{10^{17}+1}< \frac{10^{16}+1+9}{10^{17}+1+9}=\frac{10^{16}+10}{10^{17}+10}=\frac{10\left(10^{15}+1\right)}{10\left(10^{16}+1\right)}=\frac{10^{15}+1}{10^{16}+1}=A\)
\(\Rightarrow A>B\)
1)
a)
\(\frac{-5}{6}.\frac{120}{25}< x< \frac{-7}{15}.\frac{9}{14}\)
\(\frac{-1}{1}.\frac{20}{5}< x< \frac{-1}{5}.\frac{3}{2}\)
\(\frac{-20}{5}< x< \frac{-3}{10}\)
\(\frac{-40}{10}< x< \frac{-3}{10}\)
\(\Rightarrow Z\in\left\{-4;-5;-6;-7;-8;-9;-10;...;-39\right\}\)
\(=\frac{8}{9}+\frac{7}{54}-\frac{7}{10}\)
\(=\frac{55}{54}-\frac{7}{10}\)
\(=\frac{43}{135}\)
a)A=1/10+1/15+...+1/120
=2(1/20+1/30+...+1/240)
=2(1/4*5+1/5*6+...+1/15*16)
=2*(1/4-1/5+1/5-1/6+...+1/15-1/16)
=2*[(1/4-1/16)+(1/5-1/5)+...+(1/15-1/15)]
=2*[(4/16-1/16)+0+...+0]
=2*3/16=3/8
b) B=1+1/3+1/6+...+1/1225
=2(1/2+1/6+1/12+...+1/2450)
=2(1/1*2+1/2*3+...+1/49*50)
=2*[1-1/2+1/2-1/3+...+1/49-1/50]
=2*[(1-1/50)+(1/2-1/2)+...+(1/49-1/49)]
=2*[(50/50-1/50)+0+...+0]
=2*49/50=49/25
a,\(\frac{1}{2}A=\frac{1}{2}\left(\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+...+\frac{1}{120}\right)\)
\(\frac{1}{2}A=\frac{1}{20}+\frac{1}{30}+\frac{1}{42}+...+\frac{1}{240}\)
\(\frac{1}{2}A=\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}+...+\frac{1}{15.16}\)
\(\frac{1}{2}A=\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}+...+\frac{1}{15}-\frac{1}{16}\)
\(\frac{1}{2}A=\frac{1}{4}-\frac{1}{16}\)\(\frac{1}{2}A=\frac{3}{16}\)suy ra \(A=\frac{3}{16}:\frac{1}{2}=\frac{3}{8}\)
B thì cậu có thể làm nhiều cách
3/5 - 7/9 . 18/35 = 3/5 - 2/5 = 1/5
4/5 - 7/10 - (-4)/15 = 24/30 - 21/30 + 8/30 = 11/30
\(\frac35\) - \(\frac79\).\(\frac{18}{35}\)
= \(\frac35\) - \(\frac25\)
= \(\frac15\)
\(\frac45\) - \(\frac{7}{10}\) - \(\frac{-4}{15}\)
= \(\frac{24}{30}\) - \(\frac{21}{30}\) + \(\frac{8}{30}\)
= \(\frac{3}{30}\) + \(\frac{8}{30}\)
= \(\frac{11}{30}\)