21-3/4-4/15-4/35-4/63-4/99-4/143-4/195-4/22521-4/3-4/15-4/35-4/63-4/99-4/143-4/195-4/225应该是这样!!
问题描述：
21-3/4-4/15-4/35-4/63-4/99-4/143-4/195-4/225
21-4/3-4/15-4/35-4/63-4/99-4/143-4/195-4/225应该是这样!!
答
原式=21-4/(1*3)-4/(3*5)-……-4/(15*17)
=21-2[1-1/3+1/3-1/5……+1/15-1/17]
=21-32/17
=325/17
答
21-4/3-4/15-4/35-4/63-4/99-4/143-4/195-4/225
=21-4[1/(1*3)-1/(3*5)+1/(5*7)+1/(7*9)+...+1/(13*15)]-4/225
=21-4*[(1/2)*(1/1-1/3+)(1/2)*(1/3-1/5)+(1/2)*(1/5-1/7)+...+(1/2)*(1/13-1/15)]-4/225
=21-2(1-1/3+1/3-1/5+1/5-1/7+...+1/13-1/15)-4/225
=21-2(1-1/15)-4/225
=21-28/15-4/225
=21-424/225
=4301/225.
答
原式=21-4/(1*3)-4/(3*5)-……-4/(15*17)
=21-2[1-1/3+1/3-1/5……+1/15-1/17]
=21-32/17
=325/17
你可能是抄错了,最后一个数应该是225