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\(11-12+13-14+15-16+17-18+19-20+21+22\)
\(=\left(11+13+15+17+19+21+22\right)-\left(12+14+16+18+20\right)\)
\(=\left(A+22\right)-B\)
số số hạng của tổng A là :
( 21 - 11 ) :2 + 1 = 6 ( số )
vậy tổng A là :
( 21 + 11 ) * 6 :2 = 96
số số hạng của tổng B là :
(20-12 ) :2 +1 = 5 ( số )
tổng B là :
( 20 + 12 ) * 5 :2 = 80
vậy \(\left(A+22\right)-B\)
\(=\left(96+22\right)-80\)
\(=118-80\)
\(=38\)
\(11-12+13-14+15-16+17-18+19-20+21+22\)
\(=\left(11-12\right)+\left(13-14\right)+\left(15-16\right)+\left(17-18\right)+\left(19-20\right)+21+22\)
\(=-1+-1+-1+-1+-1+21+22\)
\(=-5+21+22\)
\(=38.\)
\(a,\dfrac{13}{19}+\dfrac{18}{19}+\dfrac{17}{19}=\dfrac{13+18+17}{19}=\dfrac{48}{19}\\ b,\dfrac{3}{5}+\dfrac{3}{16}+\dfrac{13}{16}=\dfrac{3}{5}+\left(\dfrac{3}{16}+\dfrac{13}{16}\right)=\dfrac{3}{5}+\dfrac{16}{16}=\dfrac{3}{5}+1=\dfrac{3}{5}+\dfrac{5}{5}=\dfrac{8}{5}\)
\(a\dfrac{13+18+17}{19}=\dfrac{48}{19}\)
\(b\dfrac{3}{5}+\dfrac{3+13}{16}=\dfrac{3}{5}+1=\dfrac{3}{5}+\dfrac{5}{5}=\dfrac{8}{5}\)
1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20
=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+20+10
=20+20+20+20+20+20+20+20+20+20+10
=20×10+10
=200+10
=210
= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) + (4 + 16 ) + ( 5 + 15 ) + ( 6 + 14 ) + ( 7 + 13 ) + ( 8 + 12) + ( 9+ 11 ) + 20
= 20 + 20 + 20 +20 + 20 +20 + 20 + 20 + 20 +20
= 20 x 10
= 200
tui đầu tiên đó
(20+10)-(11+19)+(12+18)-(13+17)+(14+16)-15
=30-30+30-30-15+30
=15
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
= 15
$#Shả$
`A)=5/17xx(15/34+19/34)`
`=5/17xx1=5/17`
`B)=(13/12+7/12)+1/3`
`=5/3+1/3=2`
a,17/23 + (1 - 17/23)
= 17/23 + 6/23
= 23/23 = 1
b,17/12 + 9/7 - (2/7 + 5 /12)
= (17/12 - 5/12) + (9/7 + 2/7)
= 1+1 = 2
c, 7/13 - ( 4/7 -6/13 )
= 7/13 - 4/7+ 6/13
= (7/13 + 6/13) -4/7
= 13/13 -4/7
= 1 -4/7 = 3/7
hok tốt✍️ ✍️
a) 17/23+(1-17/23)
=17/23+1-17/23
=1
b)17/12+9/7-(2/7+5/12)
=17/12+9/7-2/7-5/12
=1+1
=2
c)
7/13-(4/7-6/13)
=7/13-4/7+6/13
=1-4/7
=3/7
a: \(3+\dfrac{21}{19}+\dfrac{17}{19}=3+\dfrac{38}{19}=3+2=5\)
b: \(\dfrac{7}{18}+\dfrac{1}{12}+\dfrac{5}{18}=\left(\dfrac{7}{18}+\dfrac{5}{18}\right)+\dfrac{1}{12}=\dfrac{12}{18}+\dfrac{1}{12}\)
\(=\dfrac{2}{3}+\dfrac{1}{12}=\dfrac{8}{12}+\dfrac{1}{12}=\dfrac{9}{12}=\dfrac{3}{4}\)
a) =3+(21/19+17/19)
=3+2
=5
b) =(7/18+5/18)+1/12
=2/3+1/12
=8/12+1/12
=9/12=3/4