b. 1/1*2= (2-1)/1*2=2/1*2 - 1/ 1*2= 1/1 -1/2
1/2*3=1/2 -1/3
................................................................
1/99*100=1/99 -1/100
se reduc toti termenii, raman doar primul si ultimul
1/1 - 1/100=100/100 - 1/100= 99/100
(3/5)^4*(3/5) ^3: (3/5) ^5= (3/5)^7:(3/5)^5= (3/5) ^2= 9/25
99/100:9/25 = 99/100*25/9=99*25/9*100= 11/4