11/10+41/40+89/88+...+461/460
Những câu hỏi liên quan
1.Tính nkanh
a, A= 1/10 + 1/40 + 1/88 + 1/154 + 1/238 + 1/340
b, 5/6 + 11/12 + 19/20 + 41/42 + 56/56 + 71/72 + 89/90
Mjnk đang cần gấp bn nào lm dc mik tick 7 tick nka
1. (-8)+12+(-20)+(-22)+28
2. 371+731+(-271)+(-531)
3.9+(-10)+11+(-12)+13+(-14)+15+(-16)
4.[461+(-78)+40]+(-461)
5.577+[(-100)+41]+(-618)
6.[453+64+(-879)]+(-517)
2/10+2/40+2/88+...+2/340+2/460=
2/10+2/40+2/88+...+2/340+2/460=
2/10+2/40+2/88+.....+2/340+2/460
=2/2.5+2/5.8+2/8.11+....+2/17.20+2/20.23
=2/3.(3/2.5+3/5.8+3/8.11+....+3/17.20+3/20.23)
=2/3.(1/2-1/5+1/5-1/8+1/8-1/11+.....+1/17-1/20+1/20-1/23)
=2/3.(1/2-1/23)=2/3.21/46=7/23
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2/10+2/40+2/88+...+2/340+2/460
tách thành
=2/2x5+2/5x8+2/8x11+...+2/17x20+2/20x23
=2/3x(1+1/5-1/5+1/8-1/8+...+1/20-1/20+1/23)
=2/3x(1+1/23)
=2/3x24/23
=16/23
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3/10+3/40+3/88+3/154+3/238+3/340+3/460
\(\frac{3}{10}+\frac{3}{40}+\frac{3}{88}+...+\frac{3}{460}\)
\(=\frac{3}{2\cdot5}+\frac{3}{5\cdot8}+\frac{3}{8\cdot11}+...+\frac{3}{20\cdot23}\)
\(=\frac{1}{2}-\frac{1}{5}+\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+...+\frac{1}{20}-\frac{1}{23}\)
\(=\frac{1}{2}-\frac{1}{23}\)
\(=\frac{21}{46}\)
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A =\(\frac{1}{10}+\frac{1}{40}+\frac{1}{88}+.......+\frac{1}{460}\)
A=1/3x(1/2x5+1/5x8+......+1/20x23)
A=1/3x(1/2-1/5+1/5-1/8+......+1/20-1/23)
A=1/3x(1/2-1/23)
A=1/3x21/46
A=7/46
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7-8+9-10+11-12+...-86+87-88+89
\(=\left(7-8\right)+\left(9-10\right)+...+\left(87-88\right)+89\)
\(=\left(-1\right)+\left(-1\right)+...+\left(-1\right)+89\)
Số các số hạng từ 7 đến 88 là: \(88-7+1=82\) (số hạng)
\(=\left(-1\right)\cdot\left(82\div2\right)+89\)
\(=\left(-1\right)\cdot41+89\)
\(=\left(-41\right)+89\)
\(=48\)
Tính nhanh:
a)1/2+5/6+11/12+19/20+29/30+41/42+55/56+71/72+89/90
b)4/3.7+4/7.11+4/11.15+4/15.19+4/19.23+4/23.27
c)1/10+1/40+1/88+1/154+1/138+1/340
Các bạn giúp mik vs,làm ơn.ai nhanh mik tick cho.thank you very much
a)1/2 + 5/6 + 11/12 + 19/20 + 29/30 + 41/42 + 55/56 + 71/72+89/90
=1-1/2+1-1/6+1-1/12+1-1/20+1-1/30+1-1/42+1-1/56+1-1/72+1-1/90
=9 – (1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90)
=9 – [1/(1x2)+1/(2x3)+1/(3x4)+1/(4x5)+1/(5x6)+1/(6x7)+1/(7x8)+1/(8x9)+1/(9x10)]
=9 – ( 1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9+1/9-1/10)
=9 – (1 – 1/10) = 9 – 9/10 = 81/10
b)4/3.7 + 4/7.11 + 4/11.15 + 4/15.19 + 4/19.23 + 4/23.27
=4.(4/3.7 + 4/7.11 + ........+ 4/23.27 )
=1.( 1/3.7 + 1/7.11 + ......+ 1/23.27 )
=1.(1/3 - 1/7 + 1/7 - 1/11 +............ + 1/23 - 1/27 )
=1.(1/3 - 1/27 )
=1.(9/27 - 1/27)
=1.8/27
=8/27
c)1/10+1/40+1/88+1/154+1/138+1/340
=1/2.5 + 1/5.8 + 1/11.8 + 1/11.14 + 1/14.17 + 1/17.20
=1/3. (3/2.5 + 3/5.8 + 3/8.11 + 3/11.14 + 3/14.17 + 3/17.20 )
=1/3. ( 1/2 - 1/5 + 1/5 - 1/8 + 1/8 - 1/11 + 1/11 - 1/14 + 1/14 - 1/17 + 1/17 -1/20 )
=1/3. ( 1/2 - 1/20 )
=1/3. 9/20
=3/20
P/S: CHÚC HOK TỐT !
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