a=2,b=1所以慎厅原式念塌=1/1*2+1/2*3+1/3*4+……+1/2009*2010=1-1/仔孝圆2+1/2-1/3+1/3-1/4+……+1/2009-1/2010=1-1/2010=2009/2010