A

A

A

\(320-\left[32-2.\left(5-2\right)^2\right]\)

\(=320-\left[32-2.3^2\right]\)

\(=320-\left[32-2.9\right]\)

\(=320-\left[32-18\right]\)

\(=320-14\)

\(=306\)

\(\Rightarrow B.306\)

Ta có: \(A=3+3^2+3^3+...+3^{20}\)

\(\Leftrightarrow3\cdot A=3^2+3^3+3^4+...+3^{21}\)

\(\Leftrightarrow2\cdot A=3^{21}-3\)

hay \(A=\dfrac{3^{21}-3}{2}\)

Tìm x

x - 320 : 32 = 25 . 16

x - 10 = 400

x = 400 + 10

x = 410

Vậy x = 410.

Trả lời :

x-320:32 = 25.16

x-10 = 400

x = 400+10 = 410

x - 320 : 32 = 25 x 16

x - 320 : 32 = 400

x - 10 = 400

x = 400 + 10

x = 410

Hok tốt

a) 217 - 320 : 4 = 217 - 80 = 137

b) 5025 : 5 - 25 : 5 = 1005 - 5 = 1000

c) 640 : 32 + 32 = 20 + 32 = 52

d) 2180 - 180 : 2 : 9 = 2180 - 10 = 2170

a) 217 - 320 : 4 = 217 - 80 = 137

b) 5025 : 5 - 25 : 5 = 1005 - 5 = 1000

c) 640 : 32 + 32 = 20 + 32 = 52

d) 2180 - 180 : 2 : 9 = 2180 - 10 = 2170

x - 320 : 32 = 25 . 16

x - 10 = 400

x = 400 + 10

x = 410

\(=>x=\left(320:32\right)+\left(25.26\right)=10+400=410\)

\(x-10=400\)

\(x=400+10\)

\(x=410\)

\(3B=5+\left(\dfrac{5}{3}\right)+\left(\dfrac{5}{3}\right)^2+...+\left(\dfrac{5}{3}\right)^{20}\)

=>\(2B=5-\left(\dfrac{5}{3}\right)^{21}=\dfrac{5\cdot3^{21}-5}{3^{21}}\)

=>\(B=\dfrac{5\cdot3^{21}-5}{3^{21}\cdot2}\)

=> 
B
=
5
⋅
3
21
−
5
3
21
⋅
2

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   =  \(\dfrac{31^{21}-1}{2}\)