Ta có :
\(A=2+2^2+2^3+...........+2^{10}\)
\(\Leftrightarrow2A=2^2+2^3+.........+2^{11}\)
\(\Leftrightarrow2A-A=\left(2^2+2^3+......+2^{11}\right)-\left(2+2^2+....+2^{10}\right)\)
\(\Leftrightarrow A=2^{11}-2\)
\(\Leftrightarrow A+2=2^{11}\left(đpcm\right)\)
A = 2 + 22 + 23 + ... + 210
=> 2A = 22 + 23 + ... + 211
=> 2A - A = 211 - 2
=> A = 211 - 2
Thay vào bài ra ta được : 211 - 2 + 2 = 211 (đpcm)
Ta có :
A=2+22+23+.....+210
\(\Leftrightarrow\)2A=22+23+.....+211
\(\Leftrightarrow\)2A-A=(22+23+.....+211)-(2+22+23+.....+210)
\(\Leftrightarrow\)A=211-2
Vậy A+2=211
