1 + 2 + 3 + 4 + 5+ 19 +18 + 17 + 16 + 15
Bài 13: Dấu <, =, >
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
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...+15+16+17+18+19+20
1+2+3+4+5+...+15+16+17+18+19+20
= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) + ( 4 + 16 ) + ( 5 + 15 ) + ... + ( 9 + 11 ) + ( 10 + 20 )
= 20 + 20 + 20 + 20 + ... + 20 + 30
= 180 + 30 = 210
Tính số phần tử: \(\text{1+2+3+4+...+18+19+20}\)
\(=\left(20-1\right):1+1\) \(=20\)
Tổng : \(\dfrac{\left(20+1\right)\times20}{2}=210\)
(19+1)+(18+2)+(17+3)+(16+4)+(15+5)=??????
(19 + 1) + (18 + 2) + (17 + 3) + (16 + 4) + (15 + 5)
= 20 + 20 + 20 + 20 + 20
= 20 x 5 = 100
A= 2/1*3 - 4/3*5 + 6/5*7 - ...-16/15*17+ 18/17*19
Tìm A
Tính : 21 - 20 - 19 + 18 + 17 - 16 - 15 + 14 + ... + 5 - 4 - 3 + 2 + 1
(21-20)-(19-18)+(17-16)-(15-14)+...+(5-4)-(3-2)+1=1-1+1-1+...+1-1+1=(1-1)+(1-1)+...+(1-1)+1( có 10 cặp nhóm)
=0+0+...+0+0+1=1.
Giải:
\(21-20-19+18+17-16-15+14+...+5-4-3+2+1\)
\(=\left(21-20-19+18\right)+\left(17-16-15+14\right)+...+\left(5-4-3+2\right)+1\)
\(=0+0+...+0+1=1\)
Tính nhẩm:
15 - 5 = 11 - 1 = 16 - 3 =
12 - 2 = 18 - 8 = 14 - 4 =
13 - 2 = 17 - 4 = 19 - 9 =
15 - 5 = 10 11 - 1 = 10 16 - 3 = 13
12 - 2 = 10 18 - 8 = 10 14 - 4 = 10
13 - 2 = 11 17 - 4 = 13 19 - 9 = 10
1) 2) 3) 4) 5) 6) 7) 8 ) 9) / 10) 4 11) 12)
13) 14) 15)
16) 17)
18) 19)
1+2+3+4+5+6+7+8+9+10=
11+12+13+14+15+16+17+18+19+20=
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=
bạn5 bạn nào làm nhanh mình sẽ tích cho bạn đó
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
Tính 21-20+19+18-17-16+15+14-13-12+10+9-8-7+...-5-4+3+2-1