(1+1/2)(1+1/2^2)(1+1/2^4)(1+1/2^8)+1/2^15
=2*1/2*(1+1/2)(1+1/2^2)(1+1/2^4)(1+1/2^8)+1/2^15
=2*(1-1/2)(1+1/2)(1+1/2^2)(1+1/2^4)(1+1/2^8)+1/2^15
=2*(1-1/2^2)(1+1/2^2)(1+1/2^4)(1+1/2^8)+1/2^15
=2*(1-1/2^4)(1+1/2^4)(1+1/2^8)+1/2^15
=2*(1-1/2^8)(1+1/2^8)+1/2^15
=2*(1-1/2^16)+1/2^15
=2-2*1/2^16+1/2^15
=2-1/2^15+1/2^15
=22*1/2什么意思2乘以2分之1