Ôn tập toán 7
Các câu hỏi tương tự
8 Chứng minh rằng :
a) dfrac{1}{2!}+dfrac{2}{3!}+dfrac{3}{4!}+...+dfrac{99}{100!} 1 ; b) dfrac{1.2-1}{2!}+dfrac{2.3-1}{3!}+dfrac{3.4-1}{4!}+...+dfrac{99.100}{100!}
c) dfrac{1}{1.2}+dfrac{1}{3.4}+dfrac{1}{5.6}+...+dfrac{1}{49.50}dfrac{1}{26}+dfrac{1}{27}+dfrac{1}{28}+...+dfrac{1}{50}
d) dfrac{1}{3}+dfrac{1}{3^2}+dfrac{1}{3^3}+...+dfrac{1}{3^{99}} dfrac{1}{2}
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8 Chứng minh rằng :
a) \(\dfrac{1}{2!}+\dfrac{2}{3!}+\dfrac{3}{4!}+...+\dfrac{99}{100!}< 1\) ; b) \(\dfrac{1.2-1}{2!}+\dfrac{2.3-1}{3!}+\dfrac{3.4-1}{4!}+...+\dfrac{99.100}{100!}\)
c) \(\dfrac{1}{1.2}+\dfrac{1}{3.4}+\dfrac{1}{5.6}+...+\dfrac{1}{49.50}=\dfrac{1}{26}+\dfrac{1}{27}+\dfrac{1}{28}+...+\dfrac{1}{50}\)
d) \(\dfrac{1}{3}+\dfrac{1}{3^2}+\dfrac{1}{3^3}+...+\dfrac{1}{3^{99}}< \dfrac{1}{2}\)
ĐỀ 2:
1. Tính:
A. left(-dfrac{2}{3}right)^2+left(-dfrac{7}{8}right)+left(-dfrac{11}{12}right)
B. left(dfrac{-1}{3}right)^2:dfrac{1}{6}-2.left(dfrac{-1}{2}right)^3
C. dfrac{-1}{5}-left(dfrac{1}{2}+dfrac{3}{4}right)^2:dfrac{5}{8}
D. left|dfrac{-3}{2}+1,2right|+1dfrac{2}{3}:6
2. Tìm x, biết:
a. dfrac{2}{3}x-dfrac{1}{3}xdfrac{5}{12}
b. left(x-dfrac{12}{7}right):1dfrac{1}{5}dfrac{4}{7}
c. dfrac{2}{5}+left|x+1right|dfrac{3}{4}
3. Tìm x, y biết:
a. dfrac{x}{18}dfrac{y}{15}và x - y -30
b. 7...
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ĐỀ 2:
1. Tính:
A. \(\left(-\dfrac{2}{3}\right)^2+\left(-\dfrac{7}{8}\right)+\left(-\dfrac{11}{12}\right)\)
B. \(\left(\dfrac{-1}{3}\right)^2:\dfrac{1}{6}-2.\left(\dfrac{-1}{2}\right)^3\)\
C. \(\dfrac{-1}{5}-\left(\dfrac{1}{2}+\dfrac{3}{4}\right)^2:\dfrac{5}{8}\)
D. \(\left|\dfrac{-3}{2}+1,2\right|+1\dfrac{2}{3}:6\)
2. Tìm x, biết:
a. \(\dfrac{2}{3}x-\dfrac{1}{3}x=\dfrac{5}{12}\)
b. \(\left(x-\dfrac{12}{7}\right):1\dfrac{1}{5}=\dfrac{4}{7}\)
c. \(\dfrac{2}{5}+\left|x+1\right|=\dfrac{3}{4}\)
3. Tìm x, y biết:
a. \(\dfrac{x}{18}=\dfrac{y}{15}\)và x - y = -30
b. 7x = 9x và 10x - 8x = 68
c. \(\left(x-\dfrac{1}{2}\right)^{50}+\left(y+\dfrac{1}{3}\right)^{40}=0\)
* Lm nhanh nha
Tính các tổng sau:
a) A=\(\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{100}}\)
b) B=\(\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{102^2}\)
c) C=\(\dfrac{3}{1+2}+\dfrac{3}{1+2+3}+\dfrac{3}{1+2+3+4}+...+\dfrac{3}{1+2+3+...+100}\)
10 Thực hiện các phép tính sau:
a) dfrac{-2}{3}+dfrac{3}{4}-dfrac{-1}{6}+dfrac{-2}{5} b) dfrac{-2}{3}+dfrac{-1}{5}+dfrac{3}{4}-dfrac{5}{6}-dfrac{-7}{10}
c)dfrac{1}{2}-dfrac{-2}{5}+dfrac{1}{3}+dfrac{5}{7}-dfrac{-1}{6}+dfrac{-4}{35}+dfrac{1}{41} ;
d)dfrac{1}{100.99}-dfrac{1}{99.98}-dfrac{1}{98.97}-...-dfrac{1}{3.2}-dfrac{1}{2.1}
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10 Thực hiện các phép tính sau:
a) \(\dfrac{-2}{3}+\dfrac{3}{4}-\dfrac{-1}{6}+\dfrac{-2}{5}\) b) \(\dfrac{-2}{3}+\dfrac{-1}{5}+\dfrac{3}{4}-\dfrac{5}{6}-\dfrac{-7}{10}\)
c)\(\dfrac{1}{2}-\dfrac{-2}{5}+\dfrac{1}{3}+\dfrac{5}{7}-\dfrac{-1}{6}+\dfrac{-4}{35}+\dfrac{1}{41}\) ;
d)\(\dfrac{1}{100.99}-\dfrac{1}{99.98}-\dfrac{1}{98.97}-...-\dfrac{1}{3.2}-\dfrac{1}{2.1}\)
Chứng minh:
a. \(A=\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{8}-\dfrac{1}{16}+\dfrac{1}{32}-\dfrac{1}{64}< \dfrac{1}{3}\)
b.\(B=\dfrac{1}{3}-\dfrac{2}{3^2}+\dfrac{3}{3^3}-\dfrac{4}{3^4}+...+\dfrac{99}{3^{99}}< \dfrac{3}{16}\)
c. \(C=\dfrac{1}{41}+\dfrac{1}{42}+\dfrac{1}{43}+...+\dfrac{1}{79}+\dfrac{1}{80}>\dfrac{7}{12}\)
tính bằng cách thuận tiện nhất
| \(\dfrac{50-\dfrac{4}{15}+\dfrac{2}{15}-\dfrac{2}{17}}{10-\dfrac{8}{15}+\dfrac{4}{14}-\dfrac{4}{17}}\) |
Bài 1 Tìm x, y, z
a)\(\dfrac{y+z+1}{x}=\dfrac{x+z+2}{y}=\dfrac{x+y-3}{z}=\dfrac{1}{x+y+z}\)
b)\(\dfrac{2x}{3}=\dfrac{3y}{4}=\dfrac{4z}{5}\)và x+y+z=49
c)\(\dfrac{x-1}{2}=\dfrac{y-2}{3}=\dfrac{z-4}{4}\) và 2x+3y-z=50
d)\(\dfrac{x}{2}=\dfrac{y}{3}=\dfrac{z}{5}\) và xyz=810
Giải cụ thể giúp mình nhé!!!
Thực hiện các phép tính :
a) 9,6.2dfrac{1}{2}-left(2.125-1dfrac{5}{12}right):dfrac{1}{4}
b) dfrac{5}{18}-1,456:dfrac{7}{25}+4,5.dfrac{4}{5}
c) left(dfrac{1}{2}+0,8-1dfrac{1}{3}right)left(2,3right)+4dfrac{7}{25}-1,28
d) left(-5right).12:left[left(-dfrac{1}{4}right)+dfrac{1}{2}:left(-2right)right]+1dfrac{1}{3}
Đọc tiếp
Thực hiện các phép tính :
a) \(9,6.2\dfrac{1}{2}-\left(2.125-1\dfrac{5}{12}\right):\dfrac{1}{4}\)
b) \(\dfrac{5}{18}-1,456:\dfrac{7}{25}+4,5.\dfrac{4}{5}\)
c) \(\left(\dfrac{1}{2}+0,8-1\dfrac{1}{3}\right)\left(2,3\right)+4\dfrac{7}{25}-1,28\)
d) \(\left(-5\right).12:\left[\left(-\dfrac{1}{4}\right)+\dfrac{1}{2}:\left(-2\right)\right]+1\dfrac{1}{3}\)
câu 1 tìm x biết
\((-1\dfrac{1}{5}+x)\div(-3\dfrac{3}{5})=\dfrac{-7}{4}+\dfrac{1}{4}\div\dfrac{1}{8}\)
\(\dfrac{5}{7}+\dfrac{2}{3}x=\dfrac{3}{10}\)
\(-\dfrac{22}{15}x+\dfrac{1}{3}=|-\dfrac{2}{3}+\dfrac{1}{5}|\)