Question

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Answer 1

4+8+12+...+56

4*1+4*2+4*3+....+4*14

4*(1+2+3+...+14)

4*14*(14+1):2

4*14*15:2

56*15:2

28*15

420

3+6+9+...+123

3*1+3*2+3*3+...+3*41

3*(1+2+3+...+41)

3*41*(41+1):2

3*41*42:2

3*41*21

2583

3+5+7+....+31

1*2+1+2*2+1+2*3+1+...+2*15+1

2*(1+2+3+...+15)+1+.....+1(de 15 ori 1):2

2*15*(15+1)+15:2

15*16+15

255

sper că te-am ajutat. o seara frumoasa