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a)121212/424242=2/7
1999999999/9999999995=1/5
Sorry bạn mik chỉ bt làm câu a thôi!
HT~
Câu b:
\(\frac{a}{b}:\frac{c}{d}=\frac{ad}{bc}=\frac{6}{5}\Leftrightarrow5ad=6bc\)
\(\frac{a}{b}-\frac{c}{d}=\frac{ad-bc}{bd}=\frac{1}{15}\Leftrightarrow5\left(ad-bc\right)=\frac{bd}{3}\)
\(\Rightarrow5ad-5bc=\frac{bd}{3}\)
Thay vào ta có:
\(\frac{a}{b}-\frac{c}{d}=\frac{a}{b}-\frac{1}{3}=\frac{1}{15}\Leftrightarrow\frac{a}{b}=-\frac{4}{15}\)
\(A=1+\frac{1}{1+2}+\frac{1}{1+2+3}+...+\frac{1}{1+2+...+8}\)
= \(\frac{1}{\frac{1.2}{2}}+\frac{1}{\frac{2.3}{2}}+\frac{1}{\frac{3.4}{2}}+...+\frac{1}{\frac{8.9}{2}}\)
= \(\frac{2}{1.2}+\frac{2}{2.3}+\frac{2}{3.4}+...+\frac{2}{8.9}=2\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{8.9}\right)\)
\(=2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\right)=2\left(1-\frac{1}{9}\right)=2.\frac{8}{9}=\frac{16}{9}\)
\(A=1+\frac{1}{1+2}+\frac{1}{1+2+3}+...+\frac{1}{1+2+...+8}\)
\(A=\frac{1}{\frac{1.2}{2}}+\frac{1}{\frac{2.3}{2}}+\frac{1}{\frac{3.4}{2}}+...+\frac{1}{\frac{8.9}{2}}\)
\(A=\frac{2}{1.2}+\frac{2}{2.3}+\frac{2}{3.4}+...+\frac{2}{8.9}=2\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{8.9}\right)\)
\(A=2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\right)\)
\(A=2\left(1-\frac{1}{9}\right)=2.\frac{8}{9}=\frac{16}{9}\)
\(\text{Vậy A }=\frac{16}{9}\)
\(\text{#Hok tốt!}\)
Có \(P=\frac{1}{2}\times\frac{3}{4}\times\frac{5}{6}\times...\times\frac{399}{400}< \frac{2}{3}\times\frac{4}{5}\times...\times\frac{400}{401}\)
=> \(P^2< \frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\times...\times\frac{400}{401}=\frac{1}{401}< \frac{1}{400}=\frac{1}{20}\)
=> \(P< \frac{1}{20}\)(đpcm).
A=3/2-5/6+/12-9/20+11/30-13/42+15/56-17/72+19/90
A=11/10
hok tốt nha
Bài 1: Thực hiện phép tính:
\(\text{a, 1,3 + 2,5 – 4,7 + 5,6 – 4,3=}0,4\)
\(\text{b, - 5,7 + 4,2 – 8,2 + 11,7}=2\\ \)
\(\text{c, 25.(- 0,8).4.(-0,5).0,224}=8,96\)
Bài 3: Tính nhanh:
\(\text{a, -13,45 – 7,98 – 8,55}=-29,98\)
\(\text{b, 9,72 + 8,38 + 3,62}=21,72\)
\(c,\)\(\)\(\left| {45,37} \right| - \left| { - 29,73} \right| + \left( { - 12,27} \right)\)\(=45,37-29,73-12,27=3,38\)
\(\text{d, 31,71 – 7,41.15 – 2,59.15}=-118,29\)
Bài 1:
a) \(1,3+2,5-4,7+5,6-4,3\)
\(=\left(1,3+2,5+5,6\right)+\left(-4,7-4,3\right)\)
\(=9,4+\left(-9\right)\)
\(=0,4\)
b) \(-5,7+4,2-8,2+11,7\)
\(=\left(-5,7+11,7\right)+\left(4,2-8.2\right)\)
\(=6+\left(-4\right)\)
\(=2\)
c) \(25.\left(-0,8\right).4.\left(-0,5\right).0,224\)
\(=\left(25.4\right).\left(-0,8.-0,5\right).0,224\)
\(=100.0,4.0,224\)
\(=40.0,224\)
\(=8,96\)
B1 a)1,3+2,5-4,7+5,6-4,3
=(1,3-4,3)+2,5+(-4,7+5,6)
=-3+2,5+0,9
=0,4
b)-5,7+4,2-8,2+11,7
=(-5,7+11,7)+(4,2-8,2)
=6+(-4)
=2
c)25.(-0,8).4.(-0,5).0,224
=25.\(\dfrac{-4}{5}\).4.\(\dfrac{-1}{2}\).\(\dfrac{28}{125}\)
=\(\dfrac{25.\left(-4\right).2.2.\left(-1\right).28}{5.2.5.25}\)
=\(\dfrac{224}{25}\)
bài 1:
a. 1,3 + 2,5 – 4,7 + 5,6 – 4,3=0,4
b.- 5,7 + 4,2 – 8,2 + 11,7=2
c. 25.(- 0,8).4.(-0,5).0,224=8,96
bài 2:
a.
\(x-\left|-7,5\right|=1,92+2,06\)
\(\Leftrightarrow x-7,5=3,98\)
\(\Rightarrow x=11,48\)
b.
\(5x-\left(-3,7\right)=-\left|-8,6\right|+5,75\)
\(\Leftrightarrow5x-3,7=-2,85\)
\(\Rightarrow x=-\dfrac{2,85+3,7}{5}=-1,31\)
c.
\(7,2+2x=-8,8-3,92\)
\(\Leftrightarrow7,2+2x=-12,72\)
\(\Rightarrow x=\dfrac{-12,72-7,2}{2}=-9,96\)
d.
\(10,8-x=0,24+3,76\)
\(\Leftrightarrow10,8-x=4\)
\(\Rightarrow x=6,8\)
bài 3:
a.
\(-13,45-7,98-8,55=-\left(13,45+7,98+8,55\right)=-29,98\)
b.
\(9,72+8,38+3,62=18,1+3,62=21,72\)
c.
\(\left|45,37\right|-\left|-29,73\right|+\left(-12,27\right)\)
\(=45,37-29,73-12,27\)
\(=\dfrac{4537}{100}-\dfrac{2973}{100}-\dfrac{1227}{100}=3,37\)
d.
\(31,71-7,41.15-2,59.15\)
\(=31,71-[15\left(7,41+2,59\right)]=-118,29\)
B2 a) x-/-7,5/=1,92+2,06
x-7,5=3,98
x=3,98+7,5
x=11,48
b)5x-(-3,7)=-/-8,6/+5,75
5x+3,7=-8,6+5,75
5x+3,7=-2,85
5x=-2,85-3,7
5x=-6,55
x=-1,31
c)7,2+2x=-8,8-3,92
7,2+2x=-12,72
2x=-19,92
x=-9,96
d)10,8-x=0,24+3,76
10,8-x=4
x=6,8
Bài 2:
a) \(x-\left|-7,5\right|=1,92+2,06\)
\(x-7,5=3,98\)
\(x=3,98+7,5\)
\(x=11,48\)
c) \(7,2+2x=-8,8-3,92\)
\(7,2+2x=-12,08\)
\(2x=-12,08-7,2\)
\(2x=-20,88\)
\(x=-20,88:2\)
\(x=-10,44\)
d) \(10,8-x=0,24+3,76\)
\(10,8-x=4\)
\(x=10,8-4\)
\(x=6,8\)
Câu b ko có đáp án nên mk ko lm đc nha!
sai làm lại!
B3 a) -13,45-7,98-8,55
=(-13,45-8,55)-7,98
=-22-7,98
=-29,98
b)9,72+8,38+3,62
=9,72+(8,38+3,62)
=9,72+12
=21,72
c)/45,37/-/-29,37/+(-12,27)
=45,37-29,37-12,27
=(45,37-29,37)-12,27
=16-12,27
=3,37
d)31,71-7,41.15-2,59.15
=31,71+(-7,41-2,59).15
=31,71-10.15
=31,71-150
=-118,29
mơn nha
Bài 1: Thực hiện phép tính
\(a,1,3+2,5-4,7+5,6-4,3\)
= \(\left(1,3+2,5-4,7\right)\) \(+\) \(\left(5,6-4,3\right)\)
= \(-0,9+1,3\)
= \(0,4\)
\(b,-5,7+4,2-8,2+11,7\)
= \(\left(-5,7+11,7\right)\) \(-\) \(\left(4,2-8,2\right)\)
= \(6\) \(+\left(-4\right)\) = \(2\)
\(c,25.\left(-0,8\right).4.\left(0,5\right).0,224\)
= \(\left(25.4\right)\)\(.\left[\left(-0,8\right).0,5\right]\) \(.0,224\)
= \(100\) . \(\left(-0,4\right)\) . \(0,224\)
= \(-40\) . \(0,224\)
= \(-8,96\)
kcj ạ
Bài 2:
a) \(x-\left|-7,5\right|=1,92+2,06\)
\(x-7,5=3,98\)
\(x=3,98+7,5\)
\(x=11,48\)
b) \(5x-\left(-3,7\right)=-\left|-8,6\right|+5,75\)
\(5x+3,7=-8,6+5,75\)
\(5x+3,7=-2,85\)
\(5x=-2,85-3,7\)
\(5x=-6,55\)
\(x=-6,55:5\)
\(x=-1,31\)
c) \(7,2+2x=-8,8-3,92\)
\(7,2+2x=-12,72\)
\(2x=-12,72-7,2\)
\(2x=-19,92\)
\(x=-19,92:2\)
\(x=-9,96\)
d) \(10,8-x=0,24+3,76\)
\(10,8-x=4\)
\(x=10,8-4\)
\(x=6,8\)
Bài 3:
a) \(-13,45-7,98-8,55\)
\(=\left(-13,45-8,55\right)-7,98\)
\(=-22-7,98\)
\(=-29,98\)
b) \(9,72+8,38+3,62\)
\(=9,72+\left(8,38+3,62\right)\)
\(=9,72+12\)
\(=21,72\)
c) \(\left|45,37\right|-\left|29,73\right|+\left(-12,27\right)\)
\(=45,37-29,73-12,27\)
\(=45,37+\left(-29,73-12,27\right)\)
\(=45,37+\left(-42\right)\)
\(=3,37\)
d) \(31,71-7,41.15-2,59.15\)
\(=31,71+\left(-7,41-2,59\right).15\)
\(=31,71+\left(-10\right).15\)
\(=31,71+\left(-150\right)\)
\(=-118,29\)
Bài 1:
a) 1,3+2,5−4,7+5,6−4,31,3+2,5−4,7+5,6−4,3
=(1,3+2,5+5,6)+(−4,7−4,3)=(1,3+2,5+5,6)+(−4,7−4,3)
=9,4+(−9)=9,4+(−9)
=0,4=0,4
b) −5,7+4,2−8,2+11,7−5,7+4,2−8,2+11,7
=(−5,7+11,7)+(4,2−8.2)=(−5,7+11,7)+(4,2−8.2)
=6+(−4)=6+(−4)
=2=2
c) 25.(−0,8).4.(−0,5).0,22425.(−0,8).4.(−0,5).0,224
=(25.4).(−0,8.−0,5).0,224=(25.4).(−0,8.−0,5).0,224
=100.0,4.0,224=100.0,4.0,224
=40.0,224=40.0,224
=8,96
Bài 3: Tính nhanh:
a, -13,45 – 7,98 – 8,55=−29,98a, -13,45 – 7,98 – 8,55=−29,98
b, 9,72 + 8,38 + 3,62=21,72b, 9,72 + 8,38 + 3,62=21,72
c,c,|45,37|−|−29,73|+(−12,27)|45,37|−|−29,73|+(−12,27)=45,37−29,73−12,27=3,38=45,37−29,73−12,27=3,38
d, 31,71 – 7,41.15 – 2,59.15=−118,29
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câu 2 làm lại thôi!
bài tiếp mà!
mơn