Explicație pas cu pas:
A)
54+55+56+..........+172=
=(172+54)×[(172-54):1+1]:2
=226×(118:1+1):2
=226×(118+1):2
=226×119:2
=26894:2
=13447
B)
3+6+9+..........+60=
=(60+3)×[(60-3):3+1]:2
=63×(57:3+1):2
=63×(19+1):2
=63×20:2
=63×10
=630
C)
4+8+12+..........+240=
=(240+4)×[(240-4):4+1]:2
=244×(236:4+1):2
=244×(59+1):2
=244×60:2
=244×30
=7320