因为a+1/a=10, 所以(a+1/a)^2=a^2+2*a*1/a+1/a^2=a^2+1/a^2+2=10^2=100, 所以a^2+ 1/a^2=100-2=98, 所以（a-1/a)^2=a^2+1/a^2-2*a*1/a=98-2=96.
