Question

1/1*3+1/2*4+1/3*5+1/4*6+.1/18*20=

Answer 1

1/1*3=1/2(1/1-1/3),1/2*4=1/2(1/2-1/4),以此类推.1/18*20=1/2(1/18-1/20),

原式=1/2(1/1-1/3+1/2-1/4.+1/17-1/19+1/18-1/20)=1/2(1/1+1/2-1/19-1/20)=531/760