1/1×4+2又1/4×7+4又1/7×10+6又1/10×13+8又1/13×16+10又1/16×19

1/1×4+2又1/4×7+4又1/7×10+6又1/10×13+8又1/13×16+10又1/16×19
1/1×4+2又1/4×7+4又1/7×10+6又1/10×13+8又1/13×16+10又1/16×19

1/1×4+2又1/4×7+4又1/7×10+6又1/10×13+8又1/13×16+10又1/16×19
1/1×4+2又1/4×7+4又1/7×10+6又1/10×13+8又1/13×16+10又1/16×19
=1/{1*4)+1/(4*7)+1/(7*10)+1/(10*13)+1/(13*16)+1/(16*19)+(2+4+6+8+10)
=1/3(1-1/4+1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16+1/16-1/19)+30
=1/3*(1-1/19)+30
=1/3*(18/19)+30
=6/19+30
=30又6/19