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Bài 1:
a)A=(1-3+5-7)+(9-11+13-15)+...+(39-41+43-45)-47+49-51
A=-4+(-4)+..+(-4) -47+49-51
A=-48-47+49-51
A=-97
d)D=0
Bài 2:
a)2n+1 chia hết n-5
Có:n-5 chia hết n-5
=>2n-10: hết n-5
Mà 2n+1 ; hết n-5
=>[(2n+1)-(2n-10)]: hết n-5
=>(2n+1-2n+10): hết n-5
=>11:hết n-5
=>n-5 thuộc Ước của 11={-1;1;11;-11}
=>n={4;6;16;-6}
b)tương tự
c)n(n+2) : hết cho n+2
n^2+2n : hết cho n+2
=>n^2+5n-13-(n^2+2n)
=>n^2+5n-13-n^2-2n
=>3n-13:hết cho n+2
n+2 : hết cho n+2
=>3n+6 : hết n+2
mà 3n-13:hetea n+2
=>19 : hết n+2
=>n=-1;17;-21;-3
Bài 3:
x(5+y)-4y=9
x(5+y)-4(y+5)=29
(y+5)(x-4)=29
mình làm điển hình thôi, làm hết chắc "chớt"
Bài 1:
a) A = 1 - 3 + 5 -7 + 9 - 11 + ... +49-51
A = (-2) + (-2) + (-2) + ... + (-2)
A = (-2).13
A = -26
Bài 2:
a) 2n+1 chia hết cho n-5
<=> 2n-10+11 chia hết cho n-5
<=> 2(n-5)+11 chia hết cho n-5
mà 2(n-5) chia hết cho n-5 <=> 11 cũng chia hết cho n-5
<=>\(n-5\inƯ\left(11\right)=\left\{-11;-1;11\right\}\)
<=>\(n\in\left\{-6;4;6;16\right\}\)
\(a,\frac{0,75-0,6+\frac{3}{7}+\frac{3}{13}}{2,75-2,2+\frac{11}{7}+\frac{11}{13}}\)
\(=\frac{\frac{3}{4}-\frac{3}{5}+\frac{3}{7}+\frac{3}{13}}{\frac{11}{4}-\frac{11}{5}+\frac{11}{7}+\frac{11}{13}}\)
\(=\frac{3\left[\frac{1}{4}-\frac{1}{5}+\frac{1}{7}+\frac{1}{13}\right]}{11\left[\frac{1}{4}-\frac{1}{5}+\frac{1}{7}+\frac{1}{13}\right]}=\frac{3}{11}\)
Câu b tương tự
#)Giải :
b)\(\frac{5}{9}:\left(\frac{1}{3}+\frac{1}{4}\right)+\frac{5}{9}:\left(\frac{1}{9}+\frac{2}{3}\right)\)
\(=\frac{5}{9}:\frac{1}{3}+\frac{5}{9}:\frac{1}{4}+\frac{5}{9}:\frac{1}{9}+\frac{5}{9}:\frac{2}{3}\)
\(=\frac{5}{9}:\left(\frac{1}{3}+\frac{1}{4}+\frac{1}{9}+\frac{2}{3}\right)\)
\(=\frac{5}{9}:\frac{49}{36}\)
\(=\frac{20}{49}\)
1)
a) Bằng nhau.Vì\(\frac{-3}{5}=\frac{-9}{15}=\frac{9}{-15}=\frac{-9}{15}\)
b) Không bằng.Vì \(\frac{4}{3}=\frac{12}{9}>\frac{-12}{9}\)
2)
a).\(\frac{-2}{3}+\frac{4}{15}=\frac{-10}{15}+\frac{4}{15}=\frac{-6}{15}=-\frac{2}{5}\)
b) \(\frac{-9}{5}:\frac{3}{5}=\frac{-9}{5}x\frac{5}{3}=\frac{-45}{15}=-3\)
c) \(\frac{3}{7}x\frac{5}{11}+\frac{3}{7}x\frac{6}{11}=\frac{3}{7}x\left(\frac{5}{11}+\frac{6}{11}\right)=\frac{3}{7}x\frac{11}{11}=\frac{3}{7}x1=\frac{3}{7}\)
3)
a) 2x + 23 = 2016-(17+2016)
2x + 23 = 2016-17 + 2016 -2016
2x + 23 = 1999
2x = 1976
x = 988
b)
\(\frac{-2}{5}.x=2\)
\(x=2:\frac{-2}{5}\)
\(x=-5\)
- Học Tốt -
a ta co ;
13 -12 +11+10-9+8-7-6+5-4+3+2-1
=13-(12-11-10+9) +(8-7-6+5) -(4-3-2+1)
= 13 -0+0 -0
=13
a)\(\left(7\frac{4}{9}+4\frac{7}{11}\right)-3\frac{4}{9}\)=\(7\frac{4}{9}+4\frac{7}{11}-3\frac{4}{9}\)=\(\left(7\frac{4}{9}-3\frac{4}{9}\right)+4\frac{7}{11}\)= 4+\(4\frac{7}{11}\)=\(8\frac{7}{11}\)
b)\(\frac{-7}{9}.\frac{4}{11}+\frac{-7}{9}.\frac{7}{11}+5\frac{7}{9}\)=\(\frac{-7}{9}.\left(\frac{4}{11}+\frac{7}{11}\right)+5+\frac{7}{9}\)=\(\frac{-7}{9}.1+5+\frac{7}{9}\)=\(\frac{-7}{9}+\frac{7}{9}+5\)=\(\left(\frac{-7}{9}+\frac{7}{9}\right)+5\)= 0+5=5
c)\(50\%.1\frac{1}{3}.10\frac{7}{35}.0,75\)= \(\frac{1}{2}.\frac{4}{3}.10\frac{1}{5}.\frac{3}{4}\)=\(\frac{1}{2}.\frac{4}{3}.\frac{51}{5}.\frac{3}{4}\)=\(\frac{1.4.51.3}{2.3.5.4}\)=\(\frac{51}{2.5}\)=\(\frac{51}{10}\)
d)\(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{40.43}\)=\(\frac{1}{1}-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{40}-\frac{1}{43}\)=\(\frac{43}{43}-\frac{1}{43}\)=\(\frac{42}{43}\)
a) \(\left(7\frac{4}{9}+4\frac{7}{11}\right)-3\frac{4}{9}\)
\(=\left(\frac{67}{9}+\frac{51}{11}\right)-\frac{31}{9}\)
\(=\left(\frac{67}{9}-\frac{31}{9}\right)+\frac{51}{11}\)
\(=\frac{36}{9}+\frac{51}{11}\)
\(=\frac{95}{11}=8\frac{7}{11}\)
b) \(-\frac{7}{9}.\frac{4}{11}+-\frac{7}{9}.\frac{7}{11}+5\frac{7}{9}\)
\(=-\frac{7}{9}.\frac{4}{11}+-\frac{7}{9}.\frac{7}{11}+\frac{52}{9}\)
\(=-\frac{7}{9}.\left(\frac{4}{11}+\frac{7}{11}\right)+\frac{52}{9}\)
\(=-\frac{7}{9}.1+\frac{52}{9}\)
\(=-\frac{7}{9}+\frac{52}{9}\)
= 5
d) \(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+...+\frac{3}{40.43}\)
\(=1.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{40}-\frac{1}{43}\right)\)
\(=1.\left(1-\frac{1}{43}\right)\)
\(=1.\frac{42}{43}\)
\(=\frac{42}{43}\)
BÀI 1
a, \(5\times\frac{-7}{10}=\frac{-35}{10}=\frac{-7}{2}\)
b, \(\frac{4}{5}\times\frac{-7}{10}=\frac{-28}{50}=\frac{-14}{25}\)
c, \(\frac{4}{9}+\frac{4}{3}\times\frac{16}{4}=\frac{4}{9}+\frac{16}{3}=\frac{52}{9}\)
d, \(\frac{11}{22}-\frac{3}{9}\times\frac{14}{21}=\frac{11}{22}-\frac{2}{9}=\frac{55}{198}=\frac{5}{18}\)
BÀI 2
\(A=\frac{6}{13}\times\frac{5}{7}+\frac{6}{13}\times\frac{2}{7}+\frac{17}{13}\)
\(A=\frac{30}{91}+\frac{12}{91}+\frac{17}{13}\)
\(A=\frac{30}{91}+\frac{12}{91}+\frac{119}{91}\)
\(A=\frac{161}{91}=\frac{23}{13}\)
\(B=\frac{11}{15}\times\frac{4}{11}+\frac{11}{15}\times\frac{5}{11}+\frac{11}{15}\times\frac{2}{11}\)
\(B=\frac{4}{15}+\frac{1}{3}+\frac{2}{15}\)
\(B=\frac{11}{15}\)
\(C=\left(\frac{19}{64}-\frac{33}{22}+\frac{24}{51}\right)\times\left(\frac{1}{5}-\frac{1}{15}-\frac{2}{15}\right)\)
\(C=\frac{-797}{1088}\times0\)
\(C=0\)
\(D=\frac{8}{13}\times\frac{7}{12}+\frac{8}{13}\times\frac{5}{12}-\frac{1}{12}\)
\(D=\frac{14}{39}+\frac{10}{39}-\frac{1}{12}\)
\(D=\frac{83}{156}\)
bạn biết câu náy không (24 + 11) . {546 - [14 . (64 - 2^{3}3) : 2]} =
\(\frac{-7}{11}.\frac{11}{19}+\frac{-7}{11}.\frac{8}{19}+\frac{-4}{11}\)
\(=\frac{-7}{11}.\left(\frac{11}{19}+\frac{8}{19}\right)+\frac{-4}{11}\)
\(=\frac{-7}{11}.1+\frac{-4}{11}\)
\(=\frac{-7}{11}+\frac{-4}{11}=\frac{-11}{11}=-1\)
~ Hok tốt ~
Đặt \(B=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{2018.2019}\)
\(\Rightarrow B=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2018}-\frac{1}{2019}\)
\(\Rightarrow B=1-\frac{1}{2019}\)
\(\Rightarrow B=\frac{2018}{2019}\)
\(S=\frac{1}{1.2}+\frac{1}{2.3}+....+\frac{1}{2019.2020}\)
\(=\left(1-\frac{1}{2}\right)+\left(\frac{1}{2}-\frac{1}{3}\right)+...\left(\frac{1}{2019}-\frac{1}{2020}\right)\)
\(=1-\frac{1}{2020}=\frac{2019}{2020}\)