\(a)\frac{-3}{5}+\frac{7}{21}+\frac{-4}{5}+\frac{7}{5}\)

\(=\frac{7}{21}+\left(\frac{-3}{5}+\frac{-4}{5}+\frac{7}{5}\right)\)

\(=\frac{7}{21}+0=\frac{7}{21}\)

\(b)\frac{-3}{17}+\left(\frac{2}{3}+\frac{3}{17}\right)\)

\(=\frac{-3}{17}+\frac{2}{3}+\frac{3}{17}\)

\(=\left(\frac{-3}{17}+\frac{3}{17}\right)+\frac{2}{3}\)

\(=0+\frac{2}{3}=\frac{2}{3}\)

x=1 y=21

x=3 y=7

câu 

e) 99 - 97 + 95 - 93 + 91 - 89 + .... + 7 - 5 + 3 - 1 

= 2 + 2 + 2 + ..... + 2 ( có 49 số 2 ) 

= 2 x 20 

= 40 

a) 198-98+232-32

=100+200

=300

c)1326-326+538-62

=100+600

=700

a) 3⁵.9³.27²                                                        

=3⁵.(3²)³.(3³)²

=3⁵.3⁶.3⁶

=3^(5+6+6)

=3¹⁷

b) 4².2³.8²

=(2²)².2³.(2³)²

=2⁴.2³.2⁶

=2^(4+6+3)

=2¹³

c)625.125

=5⁴.5³

=5⁽⁴⁺³⁾

=5⁷

d)1000.100.10⁴

=10³.10².10⁴

=10^(3+4+2)

=10⁹

e)8⁴.16³.32

=(2³)⁴.(2⁴)³.2⁵

=2¹².2¹².2⁵

=2^(12+12+5)

=2²⁹

mik làm giúp bạn rồi nhé!!!

mình làm cho 2 bài khó thôi 

e) 22 + 23 + 24 + .... + 27 + 28 

= ( 28 + 22 ) x 7 : 2 

= 175 

f) 12 + 14 + 16 + 18 + 30 

= ( 18 + 12 ) x 4 : 2 + 30 

= 60 + 30 

= 90 

c) \(\left(20+9\frac{1}{4}\right):2\frac{1}{4}=\)

\(=\left(20+9,25\right):2,25\)

\(=29,25:2,25\)

\(=13\)

HOk tốt!!!!!!!!!!!!

c)13                                                                      d)18/5

h)1                                                                         g)1/15

Trình bày cả cách lm ạ

S=1−2+2^2−2^3+....+2^2002

2S=2−2^2+2^3−2^4+...+2^2003

2S+S=(2−2^2+2^3−2^4+...+2^2003)+(1−2+2^2−2^3+....+2^2002)

3S=2^2003+1

3S−2^2003

=2^2003+1−1

=2^2003

Bài 5  : \(S=-\left(a-b-c\right)+\left(-c+b-a\right)-\left(a+b\right)\)

\(A=-a+b+c-c+b-a-a-b=-3a+b\)

\(A=-2a-\left(a-b\right)=-2a-1\)

\(S=1-2+2^2-2^3+...+2^{2002}\)

\(2S=2-2^2+2^3-...-2^{2002}+2^{2003}\)

\(2S-S=\left(2-2^2+...+2^{2003}\right)-\left(1-2+...+2^{2002}\right)\)

\(a,\frac{3}{4}.\frac{16}{9}-\frac{7}{5}:\frac{-21}{20}\)

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

\(=\frac{8}{3}\)

\(b,2\frac{1}{3}-\frac{1}{3}.\left[\frac{-3}{2}+\left(\frac{2}{3}+0,4.5\right)\right]\)

\(=2\frac{1}{3}-\frac{1}{3}.\left[\frac{-3}{2}+\frac{8}{3}\right]\)

\(=2\frac{1}{3}-\frac{1}{3}.\frac{7}{6}\)

\(=2\frac{1}{3}-\frac{7}{18}\)

\(=\frac{35}{18}\)

\(c,\frac{32}{15}:\left(-1\frac{1}{5}+1\frac{1}{3}\right)\)

\(=\frac{32}{15}:\frac{2}{15}\)

\(=16\)