1,
原式= 1/2*3+ 1/3*4+ ...+ 1/9*10
= (1/2- 1/3)+(1/3-1/4)+...+(1/9-1/10)
= 1/2-1/10
= 2/5
2,
原式= (1/4)(1/1*2*3*4- 1/2*3*4*5)+ (1/4)(1/2*3*4*5- 1/3*4*5*6)+ ...+ (1/4)(1/6*7*8*9- 1/7*8*9*10)
= (1/4)(1/1*2*3*4- 1/7*8*9*10)
= 209/20160