Bài 1 Tính : số số hạng, tổng
a) 100-99+98-97+...+4-3+2-1
NT
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Các bạn giúp mình với Dãy số sau có bao nhiêu số hạng a 1 2 3 4 ... 98 99 100 99 98 ... 4 3 2 1.b 1 3 5 7 ... 95 97 99 100 98 96 ... 8 6 4 2 .Thanks
tính tổng
1+(-2)+3+(-4)+..+19+(-20)
1-2+3-4+..+99-100
2-4+6-8+...+48-50
-1+3-5+7-...+97-99
1+2-3-4+...+97+98-99-100
mấy bn lm theo kiểu tim số số hạng nha
tks nmn
a) 1+(-2)+3+(-4)+..+19+(-20) {có 20-1+1=20(số hạng)}
= [1+(-2)]+[3+(-4)]+..+[19+(-20)] {có 20:2 = 10(tổng)}
=(-1)+(-1)+...+(-1) {có 10 số hạng}
=(-1).10
= -10
Mấy bài còn lại cũng giống z.
1+(-2)+3+(-4)+..+19+(-20)
=[1+(-2)]+[3+(-4)]+...+[19+(-20)]
=-1 + ( -1 ) + ... + (-1) (Có 10 số -1)
=-1.10
=-10
1-2+3-4+..+99-100
=(1-2)+(3-4)+...+(99-100)
=-1+(-1)+...+(-1) (Có 50 số -1)
=-1.50
=-50
2-4+6-8+...+48-50
=(2-4)+(6-8)+...+(48-50)
=-2+(-2)+...+(-2) (Có 12,5 số -2)
=-2.12,5
=-25
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KA
30 tháng 8 2021 lúc 21:25
B2: Tính tổng
A=24+25+26+...+122 C=100-99+98-97+96-95+...+2-1
B=12+15+18+21+...+1995 D=1+3+5+7+...+2021
\(A=\dfrac{\left(\dfrac{122-24}{1}+1\right)\left(122+24\right)}{2}=7227\)
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\(B=\dfrac{\left(\dfrac{1995-12}{3}+1\right)\left(1995+12\right)}{2}=664317\)
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tính 1+2-3-4+5+6-..-96+97+98-99-100
làm theo cách ghép 4 số hạng vào 1 nhóm
=(1+98-99-100)+(2-3-4+5)+(6-7-8+9)+...+(95-96-97+98)
=-100+0+0+0+0+0.........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................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Tính tổng
A=\(1^3+2^3+3^3+...+100^3\)
B=\(2^3+4^3+...+98^3\)
C=\(1^3+3^3+5^3+...+99^3\)
D=\(1^3-2^3+3^3-4^3+...+99^3-100^3\)
a) Ta có: \(A=1^3+2^3+3^3+...+100^3\)
\(=\left(1-1\right)\cdot1\cdot\left(1+1\right)+1+\left(2-1\right)\cdot2\cdot\left(2+1\right)+2+...+\left(100-1\right)\cdot100\cdot\left(100+1\right)+100\)
\(=1+2+1\cdot2\cdot3+...+99\cdot100\cdot101\)
\(=5050+25497450\)
\(=25502500\)
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Giải giúp tớ bài này với
Cho A = 1/99+2/98+3/97+4/96+....+98/2+99/1 và B = 1/2+1/3+1/4+...+1/100
Tính tỉ số A và B
\(A=\frac{1}{99}+\frac{2}{98}+\frac{3}{97}+\frac{4}{96}+...+\frac{98}{2}+\frac{99}{1}\)
\(A=1+\left(\frac{1}{99}+1\right)+\left(\frac{2}{98}+1\right)+\left(\frac{3}{97}+1\right)+\left(\frac{4}{96}+1\right)+...+\left(\frac{98}{2}+1\right)\)
\(A=\frac{100}{100}+\frac{100}{99}+\frac{100}{98}+\frac{100}{97}+\frac{100}{96}+...+\frac{100}{2}\)
\(A=100.\left(\frac{1}{100}+\frac{1}{99}+\frac{1}{98}+...+\frac{1}{2}\right)\)
\(\Rightarrow\frac{A}{B}=\frac{100\left(\frac{1}{100}+\frac{1}{99}+\frac{1}{98}+...+\frac{1}{2}\right)}{\frac{1}{2}+\frac{1}{3}+\frac{1}{4}+...+\frac{1}{100}}=100\)
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Bài 4: Tính tổng 1) 1 + (-2) + 3 + (-4) + . . . + 19 + (-20) 2) 1 – 2 + 3 – 4 + . . . + 99 – 100 3) 2 – 4 + 6 – 8 + . . . + 48 – 50 4) – 1 + 3 – 5 + 7 - . . . . + 97 – 99 5) 1 + 2 – 3 – 4 + ... + 97 + 98 – 99 - 100
1. 1 + ( -2) +3 +(-4) + .........+ 19 + (-20)
= -1 + ( -1) +....+(-1)
= -1. 10
= -10
2. 1 – 2 + 3 – 4 + . . . + 99 – 100
= ( -1) + (-1) +....+(-1)
= -1. 50
= -50
3. 2 – 4 + 6 – 8 + . . . + 48 – 50
= (-2) + (-2) +....+ (-2)
= -2. 12 + 26
= -24 + 26
= 2
4. – 1 + 3 – 5 + 7 - . . . . + 97 – 99
= 2 + 2 +......+2
= 2.25
= 50
5. 1 + 2 – 3 – 4 + ... + 97 + 98 – 99 - 100
= (1+2-3-4) +......+ ( 97+98-99 -100)
= -4 . (-4).....(-4)
= -4. 25
= -100
NL
24 tháng 3 2021 lúc 21:01
Các bạn giúp mình với :
Dãy số sau có bao nhiêu số hạng :
a) 1 ; 2 ; 3 ; 4 ; ... ; 98 ; 99 ; 100 ; 99 ; 98; ... ; 4 ; 3 ; 2 ; 1.
b) 1 ; 3 ; 5 ; 7 ; ... ; 95 ; 97 ; 99 ; 100 ; 98 ; 96 ; ... ; 8 ; 6 ; 4 ; 2 .
Thanks!
a) cos199 số
b) có 100 số
a) 199 so hang
b) 100 so hang
Bài 1:Tính tổng
1+(-2)+3+(-4)+...+19+(-20)
1-2+3-4+..+99-100
2-4+6-8+..+48-50
-1+3-5+7-.....+97-99
1+2-3-4+....+97+98-99-100
1 + (-2) + 3 + (-4) + ... + 19 + (-20)
= [1 + (-2)] + [3 + (-4)] + ... + [19 + (-20)]
= (-1) + (-1) + ... + (-1)
có 10 số -1
= (-1).10
= -10
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1 - 2 + 3 - 4 + ... + 99 - 100
= (1 - 2) + (3 - 4) + ... + (99 - 100)
= (-1) + (-1) + ... + (-1)
có 50 số -1
= (-1).50
= -50
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