Question

3道题，详细过程

Answer 1

1/21+1/77+1/165+1/285+1/437
=（1/3-1/7+1/7-1/11+1/11-1/15+1/15-1/19+1/19-1/23）÷4
=（1/3-1/23）÷4
=20/69÷4
=5/69
7又1/7+14又1/14+28又1/28+56又1/56+112又1/112+224又1/224
=（7+14+28+56+112+224）+（1/7+1/14+1/28+1/56+1/112+1/224）
=7×（1+2+4+8+16+32）+1/7×（1+1/2+1/4+1/8+1/16+1/32）
=7×63+1/7×（2-1/32）
=441+1/7×63/32
=441+9/32
=441又9/32
4x4/3x5+6x6/5x7+8x8/7x9+10x10/9x11+12x12/11x13+14x14/13x15
=6+(1/3x5+1/5x7+1/7x9+1/9x11+1/11x13+1/13x15)
=6+(1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13+1/13-1/15)÷2
=6+(1/3-1/15)÷2
=6+4/15÷2
=6+2/15
=6又2/15