Bài 1: Tính
a, 1/2 x 2/3 x 3/4 = 1/4
b, 7/8 x 8/9 x 9/10 = 7/10
c, 5/14 x 7/15 x 28/7 = 2/3
d, 2 x 1/2 x 3 x 1/3 x 4 x 1/4 x 5 x 1/5 = 1
Bài 2: Tính
a, 7/20 - ( 5/8 - 3/5 ) = 7/20 - 1/40 = 14/40 - 1/40 = 13/40
b, 5/6 + ( 5/9 - 1/4 ) = 5/6 + 11/36 = 30/36 + 11/36 = 41/36
c, 9/10 - ( 2/5 + 3/10 ) + 7/20 = 9/10 - 7/10 + 7/20 = 2/10 + 7/20 = 4/20 + 7/20 = 11/20.
Bài 3: Tìm x:
a, 1/2 + x = 5/6
x = 5/6 - 1/2
x = 1/3
b, 5/6 - x = 1/3
x = 5/6 - 1/3
x = 1/2
c, x - 1/mấy vậy bạn
d, 1/3 x x = 1/6
x = 1/6 : 1/3
x = 1/2

a)1,5.(1/3-2/3)                         

=3/2.(-1/3)

=-1/2

b)2/5+3/5:(-3/2)=1/2

=2/3+2/5+1/2

=16/15+1/2

=47/30

c)1 và 2/5 - (-1/2)^2 + 7/10

=7/5 - 1/4 + 7/10

=23/20 + 7/10

=37/20

Bài 1: 

a: x+1/2=5/6

nên x=5/6-1/2=1/3

b: x+1/4=3/4

nên x=3/4-1/4=2/4=1/2

c: x+3/10=1/2

nên x=1/2-3/10=5/10-3/10=1/5

d: x+1/4=3/8

nên x=3/8-1/4=3/8-2/8=1/8

TOT LAM

a/A=1+2+4+8+...+1024

2A=2+4+8+16+....+2048

2A-A=(2+4+8+16+....+2048)-(1+2+4+8+...+1024)

A=2048-1

A=2047

VẬY A=2047

b/B=1+5+25+125+....+15625

5B=5+25+125+625+....+78125

5B-B=(5+25+125+625+....+78125)-(1+5+25+125+....+15625)

4B=78125-1

4B=78124

B=78124:4

B=19531

VẬY B =19531

C=1/1.2+1/2.3+1/3.4+...+1/2015.2016

C=1-1/2+1/2-1/3+1/3-1/4+...+1/2015-1/2016

=1-1/2016

=2015/2016

VẬY C=2015/2016

D/=10/1.3+10/3.5+10/5.7+....+10/2013.2015

=5(2/1.3+2/3.5+2/5.7+...+2/2013.2015)

=5(1-1/3+1/3-1/5+1/5-1/7+..+1/2013-1/2015)

=5(1-1/2015)

=5.2014/2015

=2014/403

VẬY D=2014/403

a, A = 1 + 2 + 4 + 8 +...+ 1024

   \(A=1+2+2^2+2^3+....+2^{10}\)

   \(2A=2+2^2+2^3+....+2^{10}+2^{11}\)

   \(A=1+2+2^2+2^3+....+2^{10}\)

  \(A=2^{11}-1=2047\)

b, B = 1 + 5 + 25 + 125 + ... + 15625

   \(B=1+5+5^2+5^3+....+5^6\)

   \(3B=5+5^2+5^3+....+5^6+5^7\)

   \(B=1+5+5^2+5^3+....+5^6\)

  \(2B=5^7-1\Rightarrow B=\frac{5^7-1}{2}=39062\)

d, D = 10 / 1 . 3 + 10 / 3 . 5 + 10 / 5 . 7 + ... + 10 / 2013 . 2015

\(D=\frac{10}{2}.\left(\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+...+\frac{2}{2013.2015}\right)\)

\(D=\frac{10}{2}.\left(1-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+....+\frac{1}{2013}-\frac{1}{2015}\right)\)

\(D=\frac{10}{2}.\left(1-\frac{1}{2015}\right)=5.\frac{2014}{2015}=\frac{2014}{403}\)

Câu c thì tương tự

a) A = 1 + 2 + 4 + 8 + ... + 1024

=> A = 1 + (2 + 4 + 8 + ... + 1024)

                     có 512 số hạng

=> A = 1 + [(2 + 1024) . 512 : 2]

=> A = 1 + [1026 . 512 : 2]

=> A = 1 + 262656

=> A = 262657

1.
a) \(3^4\times3^5\times3^6=3^{4+5+6}=3^{15}\)

b) \(5^2\times5^4\times5^5\times25=5^2\times5^4\times5^5\times5^2=5^{2+4+5+2}=5^{13}\)

c) \(10^8\div10^3=10^{8-3}=10^5\)

d) \(a^7\div a^2=a^{7-2}=a^5\)

2.

\(987=900+80+7\\ =9\times100+8\times10+7\\ =9\times10^2+8\times10^1+7\times10^0\)

\(2021=2000+20+1\\ =2\times1000+2\times10+1\times1\\ =2\times10^3+2\times10^1+1\times10^0\)

\(abcde=a\times10000+b\times1000+c\times100+d\times10+e\times1\\ =a\times10^4+b\times10^3+c\times10^2+d\times10^1+e\times10^0\)

còn bài 2

Câu 1:

a. 3/4+1/8=6/8+1/8=7/8

x-5/7=3/5*1/2

x-5/7=3/10

       x=3/10+5/7

       x=61/70

b.4/5+3/10=8/10+3/10=11/10

x*2/3=8/8+3/4

x*2/3=7/4

       x=7/4:2/3

       x=21/8

 Thế nha, bài này dài đó!!!! :))))

a. 2^3 . 2^2 . 2^4

= 2^9

b. 10^2 . 10^3 . 10^5

= 10^10

c. x. x^5

= x^6

d. a^3 . a^2 . a^5

= a^10

a) \(2^3.2^2.2^4\)

   \(=2^{3+2+4}\)

   \(=2^9\)

b) \(10^2.10^3.10^5\)

   \(=10^{2+3+5}\)

   \(=10^{10}\)

c) \(x.x^5=x^1.x^5=x^6\)

d) \(a^3.a^2.a^5=a^{3+2+5}=a^{10}\)

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