After listing the equations, the left and right sides can eliminate a large piece.

The writing on the paper is wrong. High school mathematics has not been done for a long time, followed by a geometric series and a constant sequence.

an+ 1 = 2+( 1-3ˇn)/ 1-3+2(n- 1)= 3ˇn/2+2n- 1/2

3ˇn stands for the n power of 3.