Nhưng bn ơiX là x^2 hay tách biệt nếu tách biệt thì là 9/49 còn nếu là x^2 thì là 3/7 nhé

\(=\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+...+\frac{1}{19}-\frac{1}{21}\right)xX=\frac{9}{7} \)\(=\left(\frac{1}{3}-\frac{1}{21}\right)xX=\frac{9}{7}\)\(=\frac{2}{7}xX=\frac{9}{7}\)

\(X=\frac{9}{7}:\frac{2}{7}\)

\(X=\frac{9}{2}\)

1+2+3+4+5+6+7+8+9+10=55

11+12+13+14+15+16+17+18+19+20=155

1+2+3+4+5+6+7+8+9+10+11+12+13+14 +15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30-50-53=362

1+2+3+4+5+6+7+8+9+10=55

11+12+13+14+15+16+17+18+19+20=155

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20+21+22+23+24+25+26+27+28+29+30-50-53=362

14 nha bạn!!!

Nhớ k đó!

=14 nha bạn

tk mk thì mk tk lại

thanks nhiều

10 - 12 + 13 - 14 + 15 - 16 + 17 - 18 + 19 

= (-2) +(-1) +(-1) +(-1) + 19 

= -2 + (-3) + 19 

= - 5 + 19 

= 14

10 < 10 + 3

11 + 2=2 + 11

9 < 10 + 9

10 = 10 + 0

17 – 4 > 14 - 3

18 – 4 >12

15 > 15 – 1

17 + 1<17 + 2

12+ 5 > 16

16 =19 - 3

15 – 4 =10 + 1

19 – 3 >11

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20

=(20+1)+(2+19)+...+(10+11) có 10 cặp số

=21+21+..+21 Có 10 số hạng

=21 x 10

=210

(20+1).20:2=210

tích

\(=\frac{20\left(21\right)}{2}=210\)

\(1+2+3+4+5+6+7+8+9+10=55\)

\(11+12+13+14+15+16+17+18+19+20=155\)

=55

=155

=438

Tích cho mình đi

= 154                   

10+12+13+14+15+16+17+18+19+20=154

=154 đúng ko

10 + 11 + 12 + 13 + 14 + 15 + 15 + 16 + 17 + 18 + 19 + 20

= ( 10 + 20 ) + ( 11 + 19 ) + ( 12 + 18 ) + ( 13 + 17 ) + ( 14 + 16 ) + ( 15 + 15 )

= 30 + 30 + 30 + 30 + 30 +30 

= 30 x 6

= 180 .

10+11+12+13+14+15+16+17+18+19+20=165

Cách 1 : 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20

= (10 + 20) + (11 + 19) + (12 + 18) + (13 + 17) + (14 + 16) + 15

= 30 + 30 + 30 + 30 + 30 + 15

= 150 + 15

= 165

Cách 2 : 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17 + 18 + 19 + 20

= \(\left(\frac{20-10}{1}+1\right)\times\frac{20+10}{2}\) 

= 11 x 15 

= 165

A = \(\dfrac{4}{1\times3}\) - \(\dfrac{8}{3\times5}\) + \(\dfrac{12}{5\times7}\) - \(\dfrac{16}{7\times9}\) + \(\dfrac{20}{9\times11}\) - \(\dfrac{24}{11\times13}\)

A = ( \(\dfrac{1}{1}+\dfrac{1}{3}\)) - ( \(\dfrac{1}{3}\) + \(\dfrac{1}{5}\)) + (\(\dfrac{1}{5}\)+ \(\dfrac{1}{7}\)) - ( \(\dfrac{1}{7}\) + \(\dfrac{1}{9}\)) +( \(\dfrac{1}{9}\)+ \(\dfrac{1}{11}\)) - (\(\dfrac{1}{11}\)+\(\dfrac{1}{13}\))

A = \(\dfrac{1}{1}+\dfrac{1}{3}\) - \(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}+\dfrac{1}{7}\) - \(\dfrac{1}{7}\) - \(\dfrac{1}{9}\) + \(\dfrac{1}{9}\) + \(\dfrac{1}{11}\) - \(\dfrac{1}{11}\) - \(\dfrac{1}{13}\)

A = \(\dfrac{1}{1}\) - \(\dfrac{1}{13}\)

A = \(\dfrac{12}{13}\)

Om op

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