(4\1x7\1+7\1x10\1+10\1x13\1+13\1x16\1) x3=3x1/4x1/7+3x1/7x1/10+...+3x1/13x1/16=1/4-1/7+1/7-1/10+1/10-1/13+1/13-1/16=1/4-1/16=3/16
a
