giúp mik nha

\(\Leftrightarrow9A=3^3+3^5+...+3^{21}\\ \Leftrightarrow9A-A=3^3+3^5+...+3^{21}-3-3^3-3^5-...-3^{19}\\ \Leftrightarrow8A=3^{21}-3\Leftrightarrow A=\dfrac{3^{21}-3}{8}\)

Đề có đúng không bạn?

\(57+\left(7-32\right)=319-\left(x+3^{19}\right)\\ \Rightarrow57-25=319-\left(x+3^{19}\right)\\ \Rightarrow32=319-\left(x+3^{19}\right)\\ \Rightarrow287=x+3^{19}\\ \Rightarrow x=3^{19}-287\)

a, 4130 + 4130 + 4130 + 319 + 319 + 319

 = 4130 × 3 + 319 × 3

 = (4130 + 319) × 3

 = 4449 × 3

 = 13347

b, 1052 + 1052 – ( 286 + 286 + 286)

 = 1052 × 2 – 286 × 3 = 2104 – 858

 = 1246

c, 2020 + 2020 + 2010 + 2010 + 56 + 56

 = 2020 × 2 + 2010 × 2 + 56 × 2

 = (2020 + 2010 + 56) × 2

 = 4086 × 2

 = 8172

d, 2830 + 2830 + 2830 + 2830 +2830 = 2830 × 5 = 14150a

3A = 3+3²+3³+3⁴+...+3²⁰+3²¹

3A - A = (3+3²+3³+3⁴+...+3²⁰+3²¹) - ( 1+3+3²+3³+...+3¹⁹+2²⁰)

2A = 3²¹-1

A   =  \(\dfrac{31^{21}-1}{2}\)

Số thứ 319 là : 100 + ( 319 - 1 ) x 1 = 418

số đó là

100 + 319 - 1 = 418

418 hoặc 420

417 + 168= 585

516 – 342= 174

319 × 3= 957

283 : 7= 40 dư 3 

\(3\times\left(\frac{1}{5\times8}+\frac{1}{8\times11}+....+\frac{1}{97\times100}+x\right)=\frac{319}{100}\)

\(\Rightarrow\left(\frac{3}{5\times8}+\frac{3}{8\times11}+\frac{3}{11\times14}+...+\frac{3}{97\times100}\right)+3\times x=\frac{319}{100}\)

\(\Rightarrow\frac{1}{5}-\frac{1}{8}+\frac{1}{8}-\frac{1}{11}+\frac{1}{11}-\frac{1}{14}+...+\frac{1}{97}-\frac{1}{100}+3\times x=\frac{319}{100}\)

\(\Rightarrow\frac{1}{5}-\frac{1}{100}+3\times x=\frac{319}{100}\)

\(\Rightarrow\frac{19}{100}+3\times x=\frac{319}{100}\)

\(\Rightarrow3\times x=\frac{319}{100}-\frac{19}{100}\)

\(\Rightarrow3\times x=3\)

\(\Rightarrow x=3:3\)

\(\Rightarrow x=1\)

Vậy x = 1