Răspuns:
1+2+3+... +n = n(n+1)/2
a) 25*26/2=13*25 = 325
b)2(1+2+3+4.......+16)=2*16*17/2=16*17=272
c) 40+46+52+....+592=
d)1+3+5+7+...63=1+2+3+4+5+6+....63-(2+4+6+8+...62)=63*64/2-2(1+2+3+...31)=32*63-2*31*32/2=32*63-31*32=32(63-31)=32*32=1024
e) 13+14+15+...27 = 1+2+...+27-(1+2+...12)=27*28/2-12*13/2=378-78=300
Explicație pas cu pas: