a) \(\frac{18}{45}-\frac{4}{12}-\frac{6}{9}-\frac{21}{35}=\frac{2}{5}-\frac{1}{3}-\frac{2}{3}-\frac{3}{5}\)

\(=\left(\frac{2}{5}-\frac{3}{5}\right)-\left(\frac{1}{3}+\frac{2}{3}\right)\)

\(=\frac{-1}{3}-1\)

\(=\frac{-4}{3}\)

b) \(\frac{4}{3}+\frac{3}{5}+\frac{7}{3}+\frac{2}{5}+\frac{1}{3}=\left(\frac{4}{3}+\frac{7}{3}+\frac{1}{3}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

\(=4+1=5\)

c) \(\frac{1}{3}.\frac{4}{5}.\frac{1}{3}.\frac{6}{5}=\frac{8}{75}\)

d) \(\frac{6}{7}.\frac{8}{13}+\frac{6}{7}.\frac{9}{13}-\frac{3}{13}.\frac{6}{7}\)

\(=\frac{6}{7}.\left(\frac{8}{13}+\frac{9}{13}-\frac{3}{13}\right)\)

\(=\frac{6}{7}.\frac{14}{13}\)

\(=\frac{12}{13}\)

Mai mình phải nộp bài nên  nhanh giúp mình ạ😅

1.Tìm x , biết

.2x -1/2-1/6-1/12-...- 1/49*50=7-1/50+x

=> 2x- ( 1/2+1/6+1/12+...1/ 49.50 )= 7-1/50+x

=> 2x -( 1/1.2 + 1/2.3+1/3.4+...+1/49.50)= 7-1/50+x

=> 2x - ( 1- 1/2+ 1/2-1/3+1/3-1/4+...+1/49-1/50) = 7-1/50 + x

=> 2x - ( 1-1/50) =7-1/50 + x

=> 2x- 1+ 1/50=7-1/50+ x

=> 1+1/50= 2x- (7 - 1/50+ x)

=> 1+1/50 = 2x- 7 + 1/50- x

=> 1+1/50 = x + 1/50 - 7

=> 1 = x + 1/50 - 7 - 1/50

=> 1 = x - 7

=> x = 8 

Vậy...

Tham khảo thêm:Câu hỏi của Cừu beta - Toán lớp 7 - Học toán với OnlineMath

LinkCâu hỏi của Cừu beta - Toán lớp 7 - Học toán với OnlineMath

\(\text{2x -1/2-1/6-1/12-...- 1/49*50=7-1/50+x }\)

=> \(\text{2x- ( 1/2+1/6+1/12+...1/ 49.50 )= 7-1/50+x }\)

=> \(\text{2x -( 1/1.2 + 1/2.3+1/3.4+...+1/49.50)= 7-1/50+x }\)

=>\(\text{ 2x - ( 1- 1/2+ 1/2-1/3+1/3-1/4+...+1/49-1/50) = 7-1/50 + x}\)

=> \(\text{2x - ( 1-1/50) =7-1/50 + x }\)

=>\(\text{ 2x- 1+ 1/50=7-1/50+ x }\)

=> \(\text{1+1/50= 2x- (7 - 1/50+ x) }\)

=>\(\text{ 1+1/50 = 2x- 7 + 1/50- x}\)

=>\(\text{ 1+1/50 = x + 1/50 - 7 }\)

=>\(\text{ 1 = x + 1/50 - 7 - 1/50 }\)

=> \(\text{1 = x - 7}\)

=> \(\text{x = 8 }\)