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đơn giản :
A=\(\frac{1}{1.2}\)+\(\frac{1}{2.3}\)+\(\frac{1}{3.4}\)+........+\(\frac{1}{99.100}\)
A= \(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+.....+\frac{1}{99}-\frac{1}{100}\)
A=1 - \(\frac{1}{100}\)
A= \(\frac{99}{100}\)
CÓ AI DÙNG HỌC 24 GIỜ KO
A = 1/2 + 1/6 / + 1/ 12 + 1/20 + ......+ 1/(99.100)
A= 1/ ( 1 x 2 ) + 1/ ( 2 x 3 ) + 1 / ( 3 x 4 ) + .....+ 1/ ( 99 x 100 )
A = 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + .................+ 1/99 - 1/100
A= 1 - 1/100
A= 99/100
CHÚC BẠN HỌC TỐT
3/4 x 8/9 x 15/16 x ... x 99/100 x 120/121 = 3 x 8 x 15 x 99 x 120/ 4 x 9 x 16 x 100 x 121
= ( 1 x 3 ) x ( 2 x 4 ) x ( 3 x 5 ) x ... x ( 9 x 11 ) x ( 10 x 12 ) / ( 2 x 2 ) x ( 3 x 3 ) x ( 4 x 4 ) x ... x ( 10 x 10 ) x ( 11 x 11 )
= ( 1 x 2 x 3 x ... x 10 ) x ( 3 x 4 x 5 x ... x 12 ) / ( 2 x 3 x ... x 11 ) x ( 2 x 3 x ... x 11 ) = 12/11x2 = 6/11
\(S=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(S=\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+...+\frac{1}{9\times10}\)
\(S=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(S=1-\frac{1}{10}\)
\(S=\frac{9}{10}\)
\(S=\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{90}\)
\(S=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{9.10}\)
\(S=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{9}-\frac{1}{10}\)
\(S=1-\frac{1}{10}\)
\(S=\frac{9}{10}\)
\(\frac{1}{2}:0,5-\frac{1}{4}:0,25+\frac{1}{8}:0,125+25\%+\frac{3}{4}\)
\(=1-1+1+1\)
\(=0+2=2\)
lưu ý là\(\frac{1}{2}=0,5\)
mấy số kia cũng bằng nhau nên chia ra cũng = 1
tính nhẩm được mà
\(\frac{2006x125+1000}{126x2006-1006}=\frac{2006x125+1000}{125x2006-2006-1006}=\frac{2006x125+1000}{125x2006+1000}=1\)
=\(\frac{2006x125+1000}{125x2006+2006-1006}\)
=\(\frac{2006x125+1000}{125x2006+1000}\)
=1
\(\frac{2006\cdot125+1000}{126\cdot2006-1006}=\frac{2006\cdot\left(126-1\right)+1000}{126\cdot2006-1006}\)
\(=\frac{2006\cdot126-2006+1000}{126\cdot2006-1006}\)
\(=\frac{2006\cdot126-1006}{126\cdot2006-1006}\)
\(=1\)
\(\frac{2006x125+1000}{126x2006-1006}\)
\(=\frac{2006x125+1000}{\left(125+1\right)x2006-1006}\)
\(=\frac{2006x125+1000}{125x2006+1x2006-1006}\)
\(=\frac{2006x125+1000}{125x2006+2006-1006}\)
\(=\frac{2006x125+1000}{125x2006+1000}\)
\(=1\)
Trả lời:
\(\frac{1995\times1994-1}{1993\times1995+1994}=\frac{1995\times\left(1993+1\right)-1}{1993\times1995+1994}\)
\(=\frac{1993\times1995+1995-1}{1993\times1995+1994}\)
\(=\frac{1993\times1995+1994}{1993\times1995+1994}\)
\(=1\)