（2-√2/1*2）+（3√2-2√3/2*3)+(4√3-3√4/3*4)+...+(100√99-99√100/99*100)
=1-1/2√2+1/2√-1/3√3+1/3√3-1/4√4+.+1/99√99-1/100√100
=1-1/100√100
=1-1/10
=9/10