原式=1/2(1/13-1/15)+1/2(1/15-1/17)+1/2(1/17-1/19)+...+1/2(1/37-1/39)
=1/2【1/13-1/15+1/15-1/17+1/17-1/19+.+1/37-1/39】
=1/2【1/13-1/39】
=1/2×2/39
=1/39
謝謝,就是想知道轉(zhuǎn)成1/2(...)這一步是怎么做的~因為;1/13-1/15=2/(13×15);
所以;1/2(1/13-1/15)=1/(13×15)
原式=1/2(1/13-1/15)+1/2(1/15-1/17)+1/2(1/17-1/19)+...+1/2(1/37-1/39)
=1/2【1/13-1/15+1/15-1/17+1/17-1/19+.+1/37-1/39】
=1/2【1/13-1/39】
=1/2×2/39
=1/39
謝謝,就是想知道轉(zhuǎn)成1/2(...)這一步是怎么做的~因為;1/13-1/15=2/(13×15);
所以;1/2(1/13-1/15)=1/(13×15)