Question

nr x aparține N, știind ca 35+35*2+...+49*35=x*x*x
*=ori

Answer 1

scoti factor comun pe 35 si ai :
35*(1+2+3+...+49)=x^3 <=>
<=> 35*(1+49)*49/2 =x^3<=>
<=>35*50*49/2=x^3=>
<=> 35*25*49=x^3<=>
<=>5*7*5*5*7*7=x^3<=>
<=>5^3 *7^3 =x^3 <=>
<=>(5*7)^3 =x^3 <=>
<=>5*7=x <=>
<=>x=35

<=> =daca si numai daca
/ =impartit
^ = la puterea