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Cho tg tren la A
A=\(\frac{1}{4}+\frac{1}{12}+\frac{1}{24}+\frac{1}{40}+\frac{1}{60}+\frac{1}{84}\)
\(A=2\left(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+\frac{1}{8.10}+\frac{1}{10.12}+\frac{1}{12.14}\right)\)
\(A=2\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+\frac{1}{8}-\frac{1}{10}+\frac{1}{10}-\frac{1}{12}+\frac{1}{12}-\frac{1}{14}\right)\)
\(A=2\left(\frac{1}{2}-\frac{1}{14}\right)\)
\(A=2.\frac{3}{7}\)
\(A=\frac{6}{7}\)
A = 1/4 + 1/12 + 1/24 + 1/40 + 1/60 + 1/84
= 2 ( 1/2*4 + 1/4*6 + 1/6*8 + 1/8*10 + 1/10*12 + 1/12*14 )
= 2 ( 1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + 1/8 - 1/10 + 1/10 - 1/12 + 1/12 - 1/14 )
= 2 ( 1/2 - 1/14 )
= 6/7
Ta co :
\(\frac{1}{4}+\frac{1}{12}+\frac{1}{24}+\frac{1}{40}+\frac{1}{60}+\frac{1}{84}\)
\(=2\left(\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+\frac{1}{8.10}+\frac{1}{10.12}+\frac{1}{12.14}\right)\)
\(=2\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+\frac{1}{8}-\frac{1}{10}+\frac{1}{10}-\frac{1}{12}+\frac{1}{12}-\frac{1}{14}\right)\)
\(=2\left(\frac{1}{2}-\frac{1}{14}\right)\)
\(=2.\frac{3}{7}\)
\(=\frac{6}{7}\)
Đặt A = 1/4 + ... +1/84
A = 2/8 + 2/24 + ... + 2/168
A = 2/2.4 + 2/4.6 + ... + 2/12.14
A = 1/2 - 1/4 + 1/4 - 1/6 + .. + 1/12 - 1/14
A = 1/2 - 1/14
A = 6/14 = 3/7
\(A=\frac{1}{4}+\frac{1}{12}+\frac{1}{24}+\frac{1}{40}+\frac{1}{60}+\frac{1}{84}\)
\(A=\frac{2}{8}+\frac{2}{24}+\frac{2}{48}+\frac{2}{80}+\frac{2}{120}+\frac{2}{168}\)
\(A=\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+\frac{2}{8.10}+\frac{2}{10.12}+\frac{2}{12.14}\)
\(A=\left(\frac{1}{2}-\frac{1}{4}\right)+\left(\frac{1}{4}-\frac{1}{6}\right)+\left(\frac{1}{6}-\frac{1}{8}\right)+\left(\frac{1}{8}-\frac{1}{10}\right)+\left(\frac{1}{10}-\frac{1}{12}\right)+\left(\frac{1}{12}-\frac{1}{14}\right)\)
\(A=\frac{1}{2}-\frac{1}{14}\)
\(A=\frac{3}{7}\)
Vậy \(\frac{1}{4}+\frac{1}{12}+\frac{1}{24}+\frac{1}{40}+\frac{1}{60}+\frac{1}{84}=\frac{3}{7}\)
\(\text{-204 + 84 : 2}\)
\(=-204+42\)
\(=-162\)
\(\text{792-24.(-2) + (-692) + (-26).(-2) }\)
\(=\left[792+\left(-692\right)\right]+\left(-2\right).\left(-24-26\right)\)
\(=100+\left(-2\right).\left(-50\right)\)
\(=-100+100=0\)
chúc bạn học tốt
số | ƯCLN | BCNN |
24 và 10 | 2 | 120 |
30 và 28 | 2 | 420 |
150 và 84 | 6 | 2100 |
11 và 15 | 1 | 165 |
30 và 90 | 30 | 90 |
140;210 và 56 | 14 | 840 |
105;84 và 30 | 3 | 420 |
14;82 và 30 | 2 | 8610 |
24;36 và 160 | 4 | 1440 |
200;125 và 75 | 25 | 1000 |
đúng thì k mình nh
2A=1/2+1/6+1/12+1/20+1/30+1/42
=1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7
=1/1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7
ta có: A = 1/4 + 1/12 + 1/24 + 1/40 + 1/60 + 1/84
= 2 ( 1/2*4 + 1/4*6 + 1/6*8 + 1/8*10 + 1/10*12 + 1/12*14 )
= 2 ( 1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + 1/8 - 1/10 + 1/10 - 1/12 + 1/12 - 1/14 )
= 2 ( 1/2 - 1/14 )
= 6/7
A= 24 + 24 +...+24 + 16 + 16+...+16
A = 24\(\times\) (1+1+...+1) + 16 \(\times\)(1 + 1+1...+1)
A = 24 \(\times\) 84 + 16 \(\times\) 24
A = 24 \(\times\)(84+16)
A = 24 \(\times\) 100
A =2400
A=24x(1+1+...+1)+16x(1+1+1+...+1)
A=24x84+16x24
A=24x(84+16)
A=2400
24(15-4)+4(24-15)
=24*15-24*4+4*24-4*15
=24*15-4*15=15(24-4)=15*20=300
tính nhanh
15.(-24)+(-24).84-24
= 15 . ( - 24 ) +(-24) .84 + ( -24 ) .1
=( 15 + 84 + 1 ) . (-24)
= 100 . ( -24 )
= _2400
thêm
A)27.(-16)+(-16).74+16
B)38.(78-59)-78.(38-59)
C) 74.(32+5)-32.(74+5)
D -17.25+34.26-17.49