Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Bài 3:
a: \(\dfrac{3}{5}-x=\dfrac{-1}{4}+\dfrac{7}{10}=\dfrac{-5}{20}+\dfrac{14}{20}=\dfrac{9}{20}\)
=>x=3/5-9/20=12/20-9/20=3/20
b: \(\dfrac{-5}{-8}-x=\dfrac{-5}{-6}+\dfrac{1}{8}\)
=>5/8-x=5/6+1/8
=>5/8-x=23/24
=>x=-1/3
c: \(8.25-x=3+\dfrac{1}{6}=\dfrac{19}{6}\)
=>x=33/4-19/6=99/12-38/12=61/12
Bài 3:
Số nghịch đảo của $x$ là: $\frac{1}{x}$.
Theo bài ra ta có:
$5.\frac{1}{x}=\frac{1}{2}$
$\frac{1}{x}=\frac{1}{2}:5=\frac{1}{10}$
$x=10$
Vậy $x=10$
Bài 2:
a)
\(\frac{7}{12}+\frac{x}{15}=\frac{1}{20}\)
\(\frac{x}{15}=\frac{1}{20}-\frac{7}{12}=\frac{-8}{15}\)
\(x=-8\)
b)
\(x=\frac{1}{2}+25\text{%}x=\frac{1}{2}+\frac{x}{4}\)
\(\frac{3}{4}x=\frac{1}{2}\)
\(x=\frac{1}{2}:\frac{3}{4}=\frac{2}{3}\)
c)
\(x+\frac{-7}{15}=-1\frac{1}{20}=\frac{-21}{20}\)
\(x=\frac{-21}{20}+\frac{7}{15}=\frac{-7}{12}\)
Bài 2:
\(\Leftrightarrow n-1\in\left\{1;-1;2;-2;3;-3;6;-6\right\}\)
hay \(n\in\left\{2;0;3;-1;4;-2;7;-5\right\}\)
Bài 3:
a: A=1-2+3-4+...+97-98+99
=(-1)+(-1)+...+(-1)+99
=99-49=50
b: B=(1-4)+(7-10)+...+(97-100)+103
=-3x17+103
=103-51=52
\(\dfrac{5}{11}+\dfrac{23}{29}+\dfrac{17}{11}=\left(\dfrac{5}{11}+\dfrac{17}{11}\right)+\dfrac{23}{29}=2+\dfrac{23}{29}=\dfrac{29+23}{58}=\dfrac{52}{58}=\dfrac{26}{29}\)
Câu 1:
A = \(\dfrac{-7}{12}+\dfrac{11}{8}-\dfrac{5}{9}=\dfrac{-42}{72}+\dfrac{99}{72}-\dfrac{40}{72}=\dfrac{-42+99-40}{72}=\dfrac{17}{72}\)
\(B=\dfrac{1}{7}-\dfrac{8}{7}:8-3:\dfrac{3}{4}.2^2=\dfrac{1}{7}-\dfrac{8}{7}.\dfrac{1}{8}-3.\dfrac{4}{3}.4=\dfrac{1}{7}-\dfrac{1}{7}-16=0-16=-16\)
\(C=1,4.\dfrac{15}{49}-\left(\dfrac{4}{5}+\dfrac{2}{3}\right):\dfrac{11}{5}=\dfrac{7}{5}.\dfrac{15}{49}-\dfrac{22}{15}.\dfrac{5}{11}=\dfrac{3}{7}-\dfrac{2}{3}=\dfrac{9-14}{21}=-\dfrac{5}{21}\)
Vậy A=\(\dfrac{17}{72};B=-16;C=\dfrac{-5}{21}\)
Câu 2:
a. \(\dfrac{-11x}{12}+\dfrac{3}{4}=-\dfrac{1}{6}\)
\(\Rightarrow\dfrac{-11x}{12}=-\dfrac{1}{6}-\dfrac{3}{4}\)
\(\Rightarrow\dfrac{-11x}{12}=\dfrac{-2}{12}-\dfrac{9}{12}\)
\(\Rightarrow\dfrac{-11x}{12}=\dfrac{-11}{12}\)
\(\Rightarrow-11x=\dfrac{-11.12}{12}\)
\(\Rightarrow-11x=-11\Rightarrow x=1\)
Vậy x=1
b. \(3-(\dfrac{1}{6}-x).\dfrac{2}{3}=\dfrac{2}{3}\Rightarrow3-\left(\dfrac{1}{6}-x\right)=1\)
\(\Rightarrow-(\dfrac{1}{6}-x)=1-3\Rightarrow\dfrac{1}{6}+x=-2\)
\(\Rightarrow x=2-\dfrac{1}{6}\Rightarrow x=\dfrac{11}{6}\)
Vậy x = \(\dfrac{11}{6}\)
Câu 4:
Ta có: \(\dfrac{1}{2.3}=\dfrac{1}{6}\)
\(\dfrac{1}{2}-\dfrac{1}{3}=\dfrac{3}{6}-\dfrac{2}{6}=\dfrac{1}{6}\)
\(\Rightarrow\dfrac{1}{2.3}=\dfrac{1}{2}-\dfrac{1}{3}\)
Câu 2:
a: 4x-15=75-x
=>5x=90
hay x=18
b: -7|x+6|=-49
=>|x+6|=7
=>x+6=7 hoặc x+6=-7
=>x=1 hoặc x=-13
Bài 1:
5; (-23) + 105
= 105 - 23
= 82
6; 78 + (-123)
= 78 - 123
= - (123 - 78)
= - 45
bài1
1)2763 + 152 = 2915
2)-7 +(-14)
=-(14 +7)
=-21
bài 1
a,\((\)\(\dfrac{-4}{21}\)\()\)x =\(\dfrac{28}{3}\)\(\times\)\(\dfrac{3}{28}\)
\(\Leftrightarrow\)\(\dfrac{-4}{21}\) x =1
\(\Rightarrow\)x = \(\dfrac{-21}{4}\)
b, \(\dfrac{17}{33}\)x = \(\dfrac{1}{56}\)\(\times\)56
\(\Leftrightarrow\)\(\dfrac{17}{33}\)x = 1
\(\Rightarrow\)x = \(\dfrac{33}{17}\)
bài 2 :
a, A=\(\dfrac{25}{32}\)
số nghịch đảo của A là \(\dfrac{32}{25}\)
B=\(\dfrac{3}{7}\)
số nghịch đảo của B là \(\dfrac{7}{3}\)
b, gọi tổng hai số nghịch đảo 2 số đó là Q
Q= \(\dfrac{32}{25}\) +\(\dfrac{7}{3}\)=\(\dfrac{271}{75}\)