=1/3-(1/3-1/5)+3/2×(1/5-1/7)-2(1/7-1/9)+5/2×(1/9-1/11)-3(1/11-1/13)
=1/5+3/2×1/5-(3/2+2)×1/7+(5/2+2)×1/9-(3-5/2)×1/11+3×1/13
=5/2×1/5-7/2×1/7+9/2×1/9-1/2×1/11+3/13
=1/2-1/2+1/2-1/22+3/13
=196/286