计算,1/2x4+1/4x6+1/6x8+.+1/48x50=1/2×（1/2-1/4+1/4-1/6+1/6-1/8+……+1/48-1/50）=1/2×（1/2-1/50）=1/2×12/25=6/25,1/2+1/6+1/12+1/20+1/30+1/42=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7=1-1/7=6/7...