-3x = 4y; 6y = 7z và x - 2y + 3z = -48
=> x=-84
y=63
z=54

nha bạn chúc bạn học tốt nha 

-3x = 4y ; 6y = 7z và x - 2y + 3z = 48

=> x = -84 

     y = 63

     z = 54

-HT-

X=-2

chúc bn học tốt

bạn có thể làm cụ thể hơn đc ko !

=1/2014-(1/2014.2013+1/2013.2012+...+1/3.2+1/2.1)

=1/2014-(1/-1/2+1/2-1/3+...+1/2013-1/2014)

=1/2014-1+1/2014

=-1006/1007

Lm ra luôn, ko cần ghi đề nhá !!!

\(=\frac{1}{2014}-\frac{2014-2013}{2014.2013}-\frac{2013-2012}{2013.2012}-...-\frac{3-2}{3.2}-\frac{2-1}{2.1}\)

\(=\frac{1}{2014}-\left(\frac{2014}{2014.2013}-\frac{2013}{2014.2013}\right)-...-\left(\frac{3}{3.2}-\frac{2}{3.2}\right)-\left(\frac{2}{2.1}-\frac{1}{2.1}\right)\)

\(=\frac{1}{2014}+\left(\frac{1}{2014}-\frac{1}{2013}\right)+...+\left(\frac{1}{3}-\frac{1}{2}\right)+\left(\frac{1}{2}-1\right)\)

\(=\frac{1}{2007}-1\)

\(=\frac{-1006}{1007}\)

 \(\frac{3}{7}+\frac{5}{3\cdot7}+\frac{7}{3\cdot19}+\frac{9}{7\cdot19}\)

\(=\frac{3}{7}+\frac{5}{7\cdot3}+\frac{7}{3\cdot19}+\frac{9}{19\cdot7}\)

\(=4\left(\frac{3}{4\cdot7}+\frac{5}{7\cdot12}+\frac{7}{12\cdot19}+\frac{9}{19\cdot28}\right)\)

\(=4\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{12}+\frac{1}{12}-\frac{1}{19}+\frac{1}{19}-\frac{1}{28}\right)\)

\(=4\left(\frac{1}{4}-\frac{1}{28}\right)\)

\(=4\cdot\frac{3}{14}\)

\(=\frac{12}{14}=\frac{6}{7}\)

Trả lời :

\(\frac{3}{7}+\frac{5}{7}+\frac{7}{3.19}+\frac{9}{7.19}\)

\(=\frac{3}{7}+\frac{5}{7}+\frac{7}{57}+\frac{9}{133}\)

\(=\left(\frac{3}{7}+\frac{5}{7}\right)+\frac{7}{57}+\frac{9}{133}\)

\(=\frac{8}{7}+\frac{5}{57}+\frac{9}{133}\)

... 

Tự quy đồng

~HT~

\(\frac{x^2-3}{x^2-1}=\frac{x^2-1-2}{x^2-1}=\frac{x^2-1}{x^2-1}-\frac{2}{x^2-1}=1-\frac{2}{x^2-1}\)

Trả lời: Nhớ k cho tui :)

Bài 1:

a) \(8\frac{1}{3}+0,25+\frac{1}{2}-\left(3,5+2\frac{1}{2}-\frac{3}{4}\right)\)

\(=8\frac{1}{3}+0,25+\frac{1}{2}-3,5-2\frac{1}{3}+\frac{3}{4}\)

\(=\left(8\frac{1}{3}-2\frac{1}{3}\right)+\left(0,25-3,5\right)+\left(\frac{1}{2}+\frac{3}{4}\right)\)

\(=6-3,25+1.25\)

\(=4\)