a ) 1/1.3 - 2/3.5 + 3/5.7 - 4/7.9 + 5/9.11 - 6/ 11.13 + 7/13.15 - 8/15.17
=(1-2) + (3-4) + (5-6) + (7-8) / 1.3-3.5+5.7-7.9+9.11-11.13+13.15-15.17
=-1 + (-1) + (-1) + (-1) / (1.3-3.5)+(5.7-7.9)+(9.11-11.13)+(13.15-15.17)
= -4 / 3.(1-5) + 7.(5-9) + 11.(9-13) + 15.(13-17)
=-4 / 3.(-4) +7.(-4) +11.(-4) + 15.(-4)
=-4 / -4 . (3+7+11+15)
=-4 / -4 .36
=-1 / -36
=1/36