Question

bài 2:

A=4+2^2+2^3+...+2^30

Answer 1

Ta có : 

\(A=4+2^2+2^3+...+2^{30}\)

\(=>A=2^2+2^2+2^3+...+2^{30}\)

\(=>A=2^3+2^3+...+2^{30}\)

\(...\)

\(=>A=2^{29}+2^{29}+2^{30}=2^{30}+2^{30}=2^{31}\)

Answer 2

\(A=4+2^2+2^3+...+2^{30}\)

\(2A=8+2^3+2^4+....+2^{31}\)

\(2A-A=\left(2^3-2^3\right)+\left(2^4-2^4\right)+...+\left(2^{30}-2^{30}\right)+\left(8-4-2^2\right)+2^{30}\)

\(A=2^{30}\)