n=k+1时,1^3+2^3+3^3……+k^3+(k+1)^3=[(1/2)k(k+1)]^2+(k+1)^3
=(1/4)k^2(k+1)^2+(k+1)(k+1)^2=(1/4)(k^2+4k+4)(k+1)^2
=[(1/2)(k+1)(k+2)]^2
当n=k+1时,1^3+2^3+3^3……+n^3+(n+1)^3=1^3+2^3+3^3……+k^3+(k+1)^3
=k²(k+1)²/4+(k+1)^3=(k+1)²(k²+4k+4)/4=(k+1)²(k+2)²/4 故当n=k+1时也成立