a: =>x-3=9
=>x=12
b: =>10-x=-26
=>x=36
c: =>x:4-1=2
=>x:4=3
=>x=12
d: =>x^2=4
=>x=2 hoặc x=-2
e: =>(x-2)^2=100
=>x-2=10 hoặc x-2=-10
=>x=12 hoặc x=-8
Thực hiện phép tính, tính nhanh nếu có thể
a, \(\dfrac{7}{13}\) + \(\dfrac{12}{13}\) + \(\dfrac{6}{-13}\)
b, ( \(\dfrac{4}{5}\) + \(\dfrac{1}{2}\) ) x ( \(\dfrac{6}{13}\) - 2 )
c, 75% : \(\dfrac{1}{2}\) - \(2\dfrac{1}{2}\) x ( \(-1\dfrac{1}{3}\) )
d, 0,375 x \(1\dfrac{3}{5}\) + 60% x \(\dfrac{2}{7}\) + \(\dfrac{3}{5}\) x \(\dfrac{5}{7}\)
e, \(\dfrac{-5}{6}\) x \(\dfrac{7}{13}\) + \(\dfrac{19}{13}\) : \(\dfrac{6}{-5}\) + \(\dfrac{2}{5}\)
f, 1,25 x \(\dfrac{7}{9}+\dfrac{5}{4}x\dfrac{15}{9}-1\dfrac{1}{4}:\dfrac{19}{3}\)
Bài 15:
a)\(\dfrac{-2}{5}\)+\(\dfrac{4}{5}\) . x =\(\dfrac{3}{5}\)
b)\(\dfrac{-3}{7}\) - \(\dfrac{4}{7}\):x = -2
Bài 16
a) x - \(\dfrac{10}{3}\) = \(\dfrac{7}{15}\) . \(\dfrac{3}{5}\)
b) x + \(\dfrac{3}{22}\)= \(\dfrac{27}{121}\) . \(\dfrac{11}{9}\)
c) \(\dfrac{8}{23}\) . \(\dfrac{48}{24}\) - x = \(\dfrac{1}{3}\)
d) 1 - x = \(\dfrac{49}{65}\).\(\dfrac{5}{7}\)
Bài 17: tìm x
a) \(\dfrac{62}{7}\) . x = \(\dfrac{29}{9}\): \(\dfrac{3}{56}\)
b) \(\dfrac{1}{5}\) : x=\(\dfrac{1}{5}\)+\(\dfrac{1}{7}\)
bài 18:
a)\(\dfrac{2}{5}\)+\(\dfrac{3}{4}\): x =\(\dfrac{-1}{2}\)
b)\(\dfrac{5}{7}\) - \(\dfrac{2}{3}\) . x = \(\dfrac{4}{5}\)
c) \(\dfrac{1}{2}\)x + \(\dfrac{3}{5}\)x = \(\dfrac{-2}{3}\)
d) \(\dfrac{4}{7}\).x-x = \(\dfrac{-9}{14}\)
bài 19: tính
\(\dfrac{1}{1.2}\)+\(\dfrac{1}{2.3}\)+\(\dfrac{1}{3.4}\)+...+ \(\dfrac{1}{2018.2019}\)
bài 20:tìm x
\(\dfrac{1}{1.2}\)+\(\dfrac{1}{2.3}\)+...+\(\dfrac{1}{x.\left(x+1\right)}\)=\(\dfrac{2008}{2009}\)
bài 21: tìm x
\(\dfrac{x+1}{99}\)+\(\dfrac{x+2}{98}\)\(\dfrac{x+3}{97}\)\(\dfrac{x+4}{96}\)=-4
bài 22 : so sánh các phân số sau:
a) \(\dfrac{-1}{5}\)+\(\dfrac{4}{-5}\)và 1
b) \(\dfrac{3}{5}\) và \(\dfrac{2}{3}\)+\(\dfrac{-1}{5}\)
c)\(\dfrac{3}{2}\)+\(\dfrac{-4}{3}\) và \(\dfrac{1}{10}\)+\(\dfrac{-4}{5}\)
d) \(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{5}\)+\(\dfrac{1}{6}\) và 2
bài 20 : tìm x
\(\dfrac{1}{1.2}\)+\(\dfrac{1}{2.3}\)+...+ \(\dfrac{1}{x.\left(x+1\right)}\)+\(\dfrac{1}{2018.2019}\)
bài 21: tìm x
\(\dfrac{x+1}{99}\)+\(\dfrac{x+2}{98}\)+\(\dfrac{x+3}{97}\)+\(\dfrac{x+4}{96}\)=-4
bài 22: so sánh
a) \(\dfrac{-1}{5}\)+\(\dfrac{4}{-5}\) và 1
b) \(\dfrac{3}{5}\) và \(\dfrac{2}{3}\)+\(\dfrac{-1}{5}\)
c) \(\dfrac{3}{2}\)+\(\dfrac{-4}{3}\) và \(\dfrac{1}{10}\)+\(\dfrac{-4}{5}\)
d)\(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{4}\)+\(\dfrac{1}{5}\)+\(\dfrac{1}{6}\) và 2
Tìm x,y biết
a) \(\dfrac{-5}{6}.\dfrac{120}{25}< x< \dfrac{-7}{15}.\dfrac{9}{14}\)
b) \(\left(\dfrac{-5}{3}\right)^2< x< \dfrac{-24}{35}.\dfrac{-5}{6}\)
c) \(\dfrac{1}{18}< \dfrac{x}{12}< \dfrac{y}{9}< \dfrac{1}{4}\)
d) \(\dfrac{x-4}{y-3}=\dfrac{4}{3}\) và x-y = 5
Nhanh nha đến ngày 20/7
Bài 1 : Tìm các số nguyên x , biết :
a) \(\dfrac{2}{3}\left(\dfrac{1}{2}+\dfrac{3}{4}-\dfrac{1}{3}\right)\le\dfrac{x}{18}\le\dfrac{7}{13}\left(\dfrac{1}{2}-\dfrac{1}{6}\right)\)
b) \(\left(\dfrac{31}{20}-\dfrac{26}{45}\right).-\dfrac{36}{35}< x< \left(\dfrac{51}{56}+\dfrac{8}{21}+\dfrac{1}{3}\right).\dfrac{8}{13}\)
Bài 2 :
C = \(\dfrac{-1}{3}.\dfrac{141}{17}-\dfrac{39}{9}.\dfrac{-1}{7}\)
1:Tính
a) \(\left(\dfrac{1}{7}.x-\dfrac{2}{7}\right).\left(\dfrac{-1}{5}.x-\dfrac{2}{5}\right)=0\)
b) \(\dfrac{1}{6}.x+\dfrac{1}{10}.x-\dfrac{4}{5}.x+1=0\)
2:So sánh:
a) A=\(\left(\dfrac{-46}{51}.0,32.\dfrac{17}{20}\right):\dfrac{64}{75}\)
B=\(\dfrac{-10}{11}.\dfrac{8}{9}+\dfrac{7}{8}.\dfrac{10}{11}\)
b) A=\(\dfrac{-1}{3}+\dfrac{0,2-0,375+\dfrac{5}{11}}{-0,3+\dfrac{9}{16}-\dfrac{15}{22}}\)
B=\(\dfrac{-43}{51}.\dfrac{19}{80}\)
Bài 1: Tìm x:
a. \(\dfrac{3}{5}\) - 2(\(\dfrac{x}{2}\) + \(\dfrac{-5}{4}\)) = \(\dfrac{4}{6}\)
b. (\(\dfrac{x}{3}\)- \(\dfrac{1}{2}\))(2x+4) = 0
c. |\(\dfrac{x}{5}\)- 1| = \(\dfrac{1}{4}\)
d.|2x-\(\dfrac{4}{5}\)| = \(\dfrac{3}{4}\)
Bài 2: Tính:
a. \(\dfrac{3}{4\cdot6}\)+\(\dfrac{3}{6\cdot8}\)+...............+\(\dfrac{3}{82\cdot84}\)
b. \(\dfrac{5}{3\cdot7}\)+\(\dfrac{5}{7\cdot11}\)+\(\dfrac{5}{11\cdot15}\)+\(\dfrac{5}{15\cdot19}\)
Bài 3: Cho Q = \(\dfrac{3}{10}\)+\(\dfrac{3}{11}\)+\(\dfrac{3}{12}\)+\(\dfrac{3}{13}\)+\(\dfrac{3}{14}\). Chứng minh rằng 1<Q<2. Từ đó suy ra Q không phải là số tự nhiên.
Tìm x:
a,\(\left(x+\dfrac{1}{2}\right).\left(\dfrac{2}{3}-2.x\right)=0\)
b,\(\left(x+\dfrac{1}{5}\right)m\text{ũ}2+\dfrac{17}{25}=\dfrac{26}{25}\)
c,\(\dfrac{x}{3}+\dfrac{x}{7}=\dfrac{1}{7}+\dfrac{3}{14}\)
A) TÌM X, BIẾT:
\(\left(\dfrac{1}{1.101}+\dfrac{1}{2.102}+...+\dfrac{1}{10.110}\right).x=\dfrac{1}{1.11}+\dfrac{1}{2.12}+...+\dfrac{1}{100.110}\)
B) CHỨNG TỎ RẰNG:
a/ \(S=\dfrac{1}{5}+\dfrac{1}{13}+\dfrac{1}{14}+\dfrac{1}{15}+\dfrac{1}{61}+\dfrac{1}{62}+\dfrac{1}{63}< \dfrac{1}{2}\)
b/ \(S=\dfrac{1}{41}+\dfrac{1}{42}+...+\dfrac{1}{80}>\dfrac{7}{12}\)
c/ \(S=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+...+\dfrac{1}{2^{20}}< 1\)
d/ \(\dfrac{49}{100}< S=\dfrac{1}{2^2}+\dfrac{1}{3^2}+\dfrac{1}{4^2}+...+\dfrac{1}{99^2}< 1\)
C)
a/ Tìm giá trị lớn nhất của các biểu thức sau, đồng thời tìm x để các biểu thức này đạt giá trị lớn nhất:
\(A=2018-\left|10-x\right|\)
\(B=1999-\left(x+2\right)^2\)
b) Tìm giá trị nhỏ nhất của các biểu thức sau, đồng thời tìm x để các biểu thức này đạt giá trị nhỏ nhất:
\(A=\left(2x-8\right)^2+3\)
\(B=\left|x^2-25\right|-2017\)
