Explicație pas cu pas:
b)S=1/6·7+1/7·8+1/8·9+...+1/74·75
S=1/6-1/7+1/7-1/8+1/8-1/9+...+1/73-1/74+1/74-1/75
dupa cum observam termenii se reduc si ramane :
1/6-1/75=75/450-6/450=69/450
c)S=1/4·5+1/5·6+1/6·7+...+1/71·72
S=1/4-1/5+1/5-1/6+...+1/71-1/72
S=1/4-1/72
S=18/72-1/72
S=17/72
a)
S=2/1·3+2/3·5+2/5·7+...+2/97·99
S=2/1-2/3+2/3-2/5+2/5-2/7+...+2/97-2/99
S=2/1-2/99
S=198/99-2/99
S=196/99
