(3+1)(3²+1)(3⁴+1)(3的8次+1)-(3的16次÷2)
=(3-1)(3+1)(3^2+1)(3^4+1)(3^8+1)/2-3^16/2
=(3^2-1)(3^2+1)(3^4+1)(3^8+1)/2-3^16/2
=(3^4-1)(3^4+1)(3^8+1)/2-3^16/2
=(3^8-1)(3^8+1)/2
=(3^16-1)/2
=3^16/2-1/2-3^16/2
=-1/2