\(\frac{-45.58-45.42}{2+4+6+...+16+18}=\frac{-45.\left(42+58\right)}{2+4+6+...+16+18}=\frac{-45.100}{2+4+6+...+16+18}=\frac{-4500}{2+4+6+...+16+18}\)

Ta có:2+4+6+...+18

Dãy số trên có:(18-2):2+1=9(số)

Tổng dãy trên là:(18+2).9:2=90

=>\(\frac{-4500}{2+4+6+...+16+18}=-\frac{4500}{90}=-50\)

2;4;6;8;...;16;18 có : 9 số hạng

Tổng của 9 số hạng đó là :

\(\frac{\left(18+2\right).9}{2}=90\)

\(\Rightarrow A=\frac{-45.58-45.42}{2+4+6+...+16+18}\)

\(A=\frac{-45.\left(58+42\right)}{90}=\frac{-45.100}{90}=-\frac{4500}{90}\)\(=-50\)

A=45.(58-42)/2+4+6+...+16+18

A=45.16/2+4+6+...+16+18

A=720/90

A=8  cho mk nha

a) \(A=\dfrac{-45.58-45.42}{2+4+6+...+16+18}\)

\(A=-\dfrac{45\left(58+42\right)}{\dfrac{\left(18-2\right):2+1}{2}.\left(2+18\right)}\)

\(A=\dfrac{-45.100}{\dfrac{5}{2}.20}\)

\(A=-\dfrac{45.100}{50}\)

\(A=-90\)

b) \(1-\left[\left(5\dfrac{3}{8}+x-7\dfrac{5}{24}\right):\left(-16\dfrac{2}{3}\right)\right]=0\)

\(\Rightarrow\left(5\dfrac{3}{8}+x-7\dfrac{5}{24}\right):\left(-16\dfrac{2}{3}\right)=1\)

\(\Rightarrow\left(\dfrac{43}{8}+x-\dfrac{173}{24}\right):\left(-\dfrac{46}{3}\right)=1\)

\(\Rightarrow\left(\dfrac{129}{24}-\dfrac{173}{24}+x\right).\left(-\dfrac{3}{46}\right)=1\)

\(\Rightarrow\left(-\dfrac{44}{24}+x\right).\left(-\dfrac{3}{46}\right)=1\)

\(\Rightarrow\left(-\dfrac{11}{6}+x\right).\left(-\dfrac{3}{46}\right)=1\)

\(\Rightarrow-\dfrac{11}{6}+x=1.\left(-\dfrac{46}{3}\right)\)

\(\Rightarrow-\dfrac{11}{6}+x=-\dfrac{46}{3}\)

\(\Rightarrow x=-\dfrac{46}{3}+\dfrac{11}{6}\)

\(\Rightarrow x=-\dfrac{92}{6}+\dfrac{11}{6}\)

\(\Rightarrow x=-\dfrac{81}{6}\)

\(\Rightarrow x=-\dfrac{27}{2}\)

Chả hiểu cái yêu cầu..

Thôi cứ làm nhé.

Ta tách ra làm 2 phần để tính:

(1) 45.8 - 45.42 = -1530

(2) 2 + 4 + 6 +...+ 16 + 18

Số số hạng là: ( 18 - 2 ) : 2 + 1 = 9 (số)

Tổng là: ( 18 + 2 ) x 9 : 2 = 90 

Ghép lại có: \(-\frac{1530}{90}=-17\)

tính 2+4+6+...+18

daỹ tính trên có ssh là (18+2):2+1=11(ssh)

tổng bằng:(2+18).11:2=110

A=45.8+45.42/110

A=45.(8+42)/110

A=45.50/110

A=225/11

A=20 5/11(HỖN SỐ)

\(A=\frac{45.\left(8+42\right)}{\left(18+2\right).9:2}=\frac{45.50}{90}=25\)

a: 29+131+237+763

=160+1000

=1160

b: 65+327+15+73

=65+15+327+73

=80+400

=480

c: \(12+54:8-8\)

=12+3-8

=15-8

=7

d: \(45\cdot58+45\cdot42\)

\(=45\cdot\left(58+42\right)\)

\(=45\cdot100=4500\)

e: \(35\cdot34+35\cdot26+40\cdot35\)

\(=35\cdot\left(34+26+40\right)\)

\(=35\cdot100=3500\)

f: \(65\cdot25+65\cdot45+30\cdot65\)

\(=65\cdot\left(25+45+30\right)\)

\(=65\cdot100=6500\)

g: \(750:\left\lbrace32-\left\lbrack2^2+\left(5\cdot3^2-42\right)\right\rbrack\right\rbrace+100\)

\(=\frac{750}{32-\left\lbrack4+5\cdot9-42\right\rbrack}+100=\frac{750}{32-4-45+42}+100\)

\(=\frac{750}{28-3}+100\)

=750:25+100

=30+100

=130

h: \(\left\lbrace630:\left\lbrack16+3\cdot\left(6+3\cdot4\right)\right\rbrack\right\rbrace-1\)

\(=\frac{630}{16+3\cdot\left(6+12\right)}-1=\frac{630}{16+3\cdot18}-1\)

\(=\frac{630}{70}-1\)

=9-1=8

i: \(5871:\left\lbrack928-\left(247-82\right)\cdot5\right\rbrack+2175^0\)

\(=\frac{5871}{928-165\cdot5}+1\)

\(=\frac{5871}{928-825}+1=\frac{5871}{103}+1=57+1=58\)

k: \(375:\left\lbrace32-\left\lbrack4+\left(5\cdot3^2-42\right)\right\rbrack\right\rbrace-14\)

\(=\frac{375}{32-\left\lbrack4+5\cdot9-42\right\rbrack}-14\)

\(=\frac{375}{32-\left\lbrack4+45-42\right\rbrack}-14=\frac{375}{32-\left(4+3\right)}-14=\frac{375}{32-7}-14\)

\(=\frac{375}{25}-14\)

=15-14

=1

\(\Rightarrow A=\frac{45.\left(8+42\right)}{\left(18+2\right).9:2}\)

\(\Rightarrow A=\frac{45.50}{20.9:2}\)

\(\Rightarrow A=\frac{45.50}{20:2.9}\)

\(\Rightarrow A=\frac{45.50}{10.9}\)

\(\Rightarrow A=5.5=25\)

A=25 k mk ha