90 /120 = 9/12 = 3/4 

36 / 64 = 18/32= 9 /16 

90/120=3/4

36/64=9/16

ta thấy 90/120 cùng chia hết cho 3 nên phân số rút gọn là 30/40

ta thấy phân số 36/64 cùng chia hết cho 4 nên phân số rút gọn là 9/16

a) 45 x 76 + 90 x 12

= 45 x 76 + 45 x 2 x 12

= 45 x 76 + 45 x 24

= 45 x ( 76 + 24 ) 

= 45 x 100

= 4500

b) 2 x 31 x 12 + 4 x 6 x 69

= 24 x 31 + 24 x 69

= 24 x ( 31 + 69 )

= 24 x 100

= 2400

c) 36 x 28 + 36 x 82 + 64 x 69 + 64 x41

= 36 x ( 28 + 82 ) + 64 x ( 69 + 41 )

= 36 x 110 + 64 x 110

= 110 x ( 36 + 64 )

= 110 x 100

= 11 000

d) 156 ( x + 61)  = 82

=> x + 61 = \(\frac{82}{156}\)

=> x + 61 = \(\frac{41}{78}\)

=> x = \(\frac{41}{78}\)- 61

=> x = \(\frac{-4717}{78}\)

45 x 76 + 90 x 12 = 45 x 76 + 45 x 2 x 12

= 45 x 76 + 45 x 24

= 45 x (76 + 24)

= 45 x 100 

= 4500

b) 2 x 31 x 12 + 4 x  6 x 69 = 62 x 12 + 2 x 12 x 69

= 62 x 12 + 138 x 12

= (62 + 138) x 12

= 200 x 12 = 2400

a, 45 x 76 + 90 x 12

= ( 45 x 12 ) + ( 76 x 90 )

=  540     +   6840

=     7 380

c,

= 36 x ( 28 + 82 ) +  64 x ( 69 + 41 )

= 36 x  110    +   64 x 110

= 110 x ( 36 + 64 )

= 110 x 100

= 11000

=4 nhé bạn

làm sao dậy

4 nha bạn

\(\frac{1}{10}+\frac{4}{20}+\frac{9}{30}+....+\frac{81}{90}\)

\(=\frac{1}{10}+\frac{2}{10}+\frac{3}{10}+...+\frac{9}{10}\)

\(=\frac{\left(1+2+3+.....+9\right)}{10}\)

\(=\frac{45}{10}=\frac{9}{2}\)

\(S=\frac{1}{10}+\frac{2^2}{20}+\frac{3^2}{30}+....+\frac{9^2}{90}=\frac{1}{10}+\frac{2}{10}+...+\frac{9}{10}=\frac{45}{10}=\frac{9}{2}\)

          Ta có : 

           Đặt \(A=\frac{1}{10}+\frac{4}{20}+\frac{9}{30}+\frac{16}{40}+\frac{25}{50}+\frac{36}{60}+\frac{49}{70}+\frac{64}{80}+\frac{91}{90}\)

                \(A=\frac{1}{10}+\frac{2^2}{20}+\frac{3^2}{30}+\frac{4^2}{40}+\frac{5^2}{50}+\frac{6^2}{60}+\frac{7^2}{70}+\frac{8^2}{80}+\frac{9^2}{90}\)

               \(A=\frac{1}{10}+\frac{2}{10}+\frac{3}{10}+\frac{4}{10}+\frac{5}{10}+\frac{6}{10}+\frac{7}{10}+\frac{8}{10}+\frac{9}{10}\)

             \(A=\frac{45}{10}=\frac{9}{2}\)

            Ủng hộ mk nha !!! ^_^

Rút gọn tất cả các phân số ta có: 

\(\frac{1}{10}+\frac{2}{10}+\frac{3}{10}+\frac{4}{10}+\frac{5}{10}+\frac{6}{10}+\frac{7}{10}+\frac{8}{10}+\frac{9}{10}\)

\(=\frac{1+2+3+4+5+6+7+8+9}{10}=\frac{45}{10}=\frac{9}{2}\)

cam on thinh nha thank you so much

\(\frac{1}{10}+\frac{4}{20}+\frac{9}{30}+\frac{16}{40}+\frac{25}{50}+\frac{36}{60}+\frac{49}{70}+\frac{64}{80}+\frac{81}{90}\)

=\(\frac{1}{10}+\frac{2}{10}+\frac{3}{10}+\frac{4}{10}+\frac{5}{10}+\frac{6}{10}+\frac{7}{10}+\frac{8}{10}+\frac{9}{10}\)

=\(\frac{1+2+3+4+5+6+7+8+9}{10}=\frac{45}{10}=4,5\)

Chúc bn học tốt

\(=\dfrac{1}{15}+\dfrac{2}{15}+\dfrac{3}{15}+...+\dfrac{9}{15}\)

\(=\dfrac{1+2+3+...+9}{15}\)

\(=\dfrac{45}{15}=3\)

1/10 + 4/20 + 9/30 + 16/40 + 25/50 + 36/60 + 49/70 + 64/80 + 81/90 
= 1/10 + 2/10 + 3/10 + 4/10 + 5/10 + 6/10 + 7/10 + 8/10 + 9/10 
=(1+2+3+....+9) /10 
=(1+9)x9:2 /10 
=45/10=4,5 

chắc chắn đúng đó  

\(M=\frac{1}{10}+\frac{4}{20}+\frac{9}{30}+\frac{16}{40}+...+\frac{81}{90}\)

\(M=\frac{1}{10}+\frac{2}{10}+\frac{3}{10}+\frac{4}{10}+...+\frac{9}{10}\)

\(M=\frac{\left(9+1\right)\cdot\left(9-1+1\right):2}{10}\)

\(M=\frac{10\cdot9:2}{10}=4,5\)

tớ làm giống bạn kia

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