rút gọn phân số:
1, 3.13-13.18 / 15.40-80
2, (-5)^3.40. 4^3 / 135.(-2)^14.(-100)^0
3, 2929-101 / 2.1919+404
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15 tháng 3 2021
b) \(\dfrac{6\cdot9-2\cdot17}{63\cdot3-119}\)
\(=\dfrac{2\left(3\cdot9-17\right)}{7\cdot\left(3\cdot9-17\right)}\)
\(=\dfrac{2}{7}\)
24 tháng 7 2020
Trả lời:
a, \(\frac{6\times9-2\times17}{63\times3-119}=\frac{2.3\times9-2\times17}{7.9\times3-7.17}\)
\(=\frac{2\times\left(3\times9-17\right)}{7\times\left(3\times9-17\right)}\)
\(=\frac{2}{7}\)
b, \(\frac{3\times13-13\times18}{15\times40-80}=\frac{13\times\left(3-18\right)}{40\times\left(15-2\right)}\)
\(=\frac{13\times-15}{40\times13}\)
\(=\frac{-3}{8}\)
c, \(\frac{-1997.1996+1}{\left(-1995\right).\left(-1997\right)+1996}=\frac{-1997.1996+1}{\left(1-1996\right).\left(-1997\right)+1996}\)
\(=\frac{-1997.1996+1}{-1997-1996.\left(-1997\right)+1996}\)
\(=\frac{-1997.1996+1}{-1996.\left(-1997\right)-1}\)
\(=\frac{-1997.1996+1}{-\left[1996.\left(-1997\right)+1\right]}\)
\(=-1\)
d, \(\frac{3.7.13.37.39-10101}{505050-70707}=\frac{10101.39-10101}{50.10101-7.10101}\)
\(=\frac{10101.\left(39-1\right)}{10101.\left(50-7\right)}\)
\(=\frac{10101.38}{10101.43}\)
\(=\frac{38}{43}\)
18 tháng 4 2015
RÚT GỌN:
\(\frac{3.13-13.18}{15.40-80}=\frac{13.\left(3-18\right)}{15.40-40.2}=\frac{13.\left(-15\right)}{40\left(15-2\right)}=\frac{13.\left(-15\right)}{40.13}=-\frac{15}{40}=-\frac{3}{8}\)
CHỨNG MINH:
Ta thấy \(\frac{1}{101}>\frac{1}{150};\frac{1}{102}>\frac{1}{150};...;\frac{1}{149}>\frac{1}{150}\)
=>\(\frac{1}{101}+\frac{1}{102}+...+\frac{1}{150}>\frac{1}{150}.\left(150-101+1\right)=\frac{1}{150}.50=\frac{50}{150}=\frac{1}{3}\)(đpcm)
TÍNH HỢP LÝ:
B=\(\frac{5}{13}+\frac{-5}{7}-\frac{20}{41}+\frac{8}{13}+\frac{-21}{41}=\left(\frac{5}{13}+\frac{8}{13}\right)+\left(\frac{-21}{41}-\frac{20}{41}\right)+\frac{-5}{7}=1+\left(-1\right)+\frac{-5}{7}=0+\frac{-5}{7}=\frac{-5}{7}\)
NN
19 tháng 4 2017
a, \(\dfrac{25.13}{26.35}=\dfrac{5.1}{2.7}=\dfrac{5}{14}.\)
b, \(\dfrac{6.9-2.17}{63.3-119}=\dfrac{2.3.9-2.17}{9.7.3-17.7}=\dfrac{2\left(3.9-17\right)}{7\left(9.3-17\right)}=\dfrac{2}{7}.\)
c, \(\dfrac{3.13-13.18}{15.40-80}=\dfrac{13\left(3-18\right)}{15.40-40.2}=\dfrac{13.\left(-15\right)}{40\left(15-2\right)}=\dfrac{13.\left(-15\right)}{40.13}=\dfrac{-15}{40}=\dfrac{-3}{8}.\)d, \(\dfrac{2929-101}{2.1919+404}=\dfrac{29.101-101.1}{2.19.101+101.4}=\dfrac{101\left(29-1\right)}{38.101+101.4}=\dfrac{101\left(29-1\right)}{101\left(38+4\right)}=\dfrac{29-1}{38+4}=\dfrac{28}{42}=\dfrac{2}{3}.\)
(còn tiếp!!!)
~ Chúc bn học tốt!!! ~
MH
6 tháng 2 2016
\(\frac{2929-101}{2.1919+404}=\frac{29.101-101}{2.19.101+4.101}=\frac{28.101}{42.101}=\frac{2}{3}\)
28 tháng 5 2017
\(a,\dfrac{2929-101}{2.1919+404}=\dfrac{29.101-101.1}{2.19.101+4.101}\)
\(=\dfrac{101\left(29-1\right)}{101\left(2.19+4\right)}\)
\(=\dfrac{101.29}{101.42}\)
\(=\dfrac{28}{42}=\dfrac{2}{3}\)
\(b,\dfrac{\left(-5\right)^3.40.4^3}{135.\left(-2\right)^{14}.\left(-100\right)^0}=\dfrac{\left(-5\right)^3.40.4^3}{135.\left(-2\right)^{14}}\)
\(=\dfrac{40.\left(-15\right).64}{135.\left(-2\right)^{14}}\)
\(=\dfrac{5.8.3.\left(-5\right).64}{5.3.9.\left(-2\right)^{14}}\)
\(=\dfrac{8.\left(-5\right).\left(-2\right)^6}{9.\left(-2\right)^{14}}\)
\(=\dfrac{\left(-2\right)^3.5}{9.\left(-2\right)^8}=\dfrac{5}{9.\left(-2\right)^5}\)
Đặt A = \(\frac{3.13-13.18}{15.40-80}\)
=> A = \(\frac{13.\left(3-18\right)}{15.40-80}\)
=> A = \(\frac{13.\left(-15\right)}{15.40-40.2}\)
=> A = \(\frac{13.\left(-15\right)}{40.\left(15-2\right)}\)
=> A = \(\frac{13.\left(-15\right)}{40.13}\)
=> A = \(\frac{-15}{40}\)
=> A = \(\frac{-3}{8}\)
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